[exporter/natscoreexporter] Implement exporter and factory

.github/CODEOWNERS

@@ -69,6 +69,7 @@ exporter/loadbalancingexporter/                                  @open-telemetry
 exporter/logicmonitorexporter/                                   @open-telemetry/collector-contrib-approvers @bogdandrutu @khyatigandhi6 @avadhut123pisal
 exporter/logzioexporter/                                         @open-telemetry/collector-contrib-approvers @yotamloe
 exporter/mezmoexporter/                                          @open-telemetry/collector-contrib-approvers @dashpole @billmeyer @gjanco
+exporter/natscoreexporter/                                       @open-telemetry/collector-contrib-approvers @EthanKim8683
 exporter/opencensusexporter/                                     @open-telemetry/collector-contrib-approvers @open-telemetry/collector-approvers
 exporter/opensearchexporter/                                     @open-telemetry/collector-contrib-approvers @ps48
 exporter/otelarrowexporter/                                      @open-telemetry/collector-contrib-approvers @jmacd @moh-osman3 @lquerel

.github/ISSUE_TEMPLATE/beta_stability.yaml

@@ -68,6 +68,7 @@ body:
       - exporter/logicmonitor
       - exporter/logzio
       - exporter/mezmo
+      - exporter/natscore
       - exporter/opencensus
       - exporter/opensearch
       - exporter/otelarrow

.github/ISSUE_TEMPLATE/bug_report.yaml

@@ -71,6 +71,7 @@ body:
       - exporter/logicmonitor
       - exporter/logzio
       - exporter/mezmo
+      - exporter/natscore
       - exporter/opencensus
       - exporter/opensearch
       - exporter/otelarrow

.github/ISSUE_TEMPLATE/feature_request.yaml

@@ -65,6 +65,7 @@ body:
       - exporter/logicmonitor
       - exporter/logzio
       - exporter/mezmo
+      - exporter/natscore
       - exporter/opencensus
       - exporter/opensearch
       - exporter/otelarrow

.github/ISSUE_TEMPLATE/other.yaml

@@ -65,6 +65,7 @@ body:
       - exporter/logicmonitor
       - exporter/logzio
       - exporter/mezmo
+      - exporter/natscore
       - exporter/opencensus
       - exporter/opensearch
       - exporter/otelarrow

.github/ISSUE_TEMPLATE/unmaintained.yaml

@@ -70,6 +70,7 @@ body:
       - exporter/logicmonitor
       - exporter/logzio
       - exporter/mezmo
+      - exporter/natscore
       - exporter/opencensus
       - exporter/opensearch
       - exporter/otelarrow

exporter/natscoreexporter/Makefile

@@ -0,0 +1 @@
+include ../../Makefile.Common

exporter/natscoreexporter/README.md

@@ -0,0 +1,71 @@
+# NATS Core Exporter
+
+<!-- status autogenerated section -->
+| Status        |           |
+| ------------- |-----------|
+| Stability     | [development]: metrics, logs, traces   |
+| Distributions | [contrib] |
+| Issues        | [![Open issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector-contrib?query=is%3Aissue%20is%3Aopen%20label%3Aexporter%2Fnatscore%20&label=open&color=orange&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues?q=is%3Aopen+is%3Aissue+label%3Aexporter%2Fnatscore) [![Closed issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector-contrib?query=is%3Aissue%20is%3Aclosed%20label%3Aexporter%2Fnatscore%20&label=closed&color=blue&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues?q=is%3Aclosed+is%3Aissue+label%3Aexporter%2Fnatscore) |
+| Code coverage | [![codecov](https://codecov.io/github/open-telemetry/opentelemetry-collector-contrib/graph/main/badge.svg?component=exporter_natscore)](https://app.codecov.io/gh/open-telemetry/opentelemetry-collector-contrib/tree/main/?components%5B0%5D=exporter_natscore&displayType=list) |
+| [Code Owners](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/CONTRIBUTING.md#becoming-a-code-owner)    | [@EthanKim8683](https://www.github.com/EthanKim8683) |
+
+[development]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/component-stability.md#development
+[contrib]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-contrib
+<!-- end autogenerated section -->
+
+NATS Core exporter exports logs, metrics and traces to [NATS Core](https://docs.nats.io/).
+
+## Configuration
+
+The following configuration options are supported:
+
+- `endpoint` (default = nats://localhost:4222): The NATS server URL.
+- `pedantic` (default = true): The option to enable/disable [NATS pedantic mode](https://docs.nats.io/nats-concepts/subjects#pedantic-mode).
+- `tls`: See [TLS Configuration Settings](https://github.com/open-telemetry/opentelemetry-collector/blob/main/config/configtls/README.md) for the full set of available options.
+- `logs`
+  - `subject` (default = "otel_logs"): The [OTTL value expression](https://pkg.go.dev/text/template) used to construct NATS subjects for logs.
+  - `marshaler` (default = otlp_proto): The name of the built-in marshaler used to marshal logs. See [Built-in Marshalers](#built-in-marshalers).
+  - `encoding_extension`: The name of the encoding extension used to marshal logs. This configuration option is mutually exclusive with `marshaler`. See [Encoding extensions](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/extension/encoding/README.md).
+- `metrics`
+  - `subject` (default = "otel_metrics"): The [OTTL value expression](https://pkg.go.dev/text/template) used to construct NATS subjects for metrics.
+  - `marshaler` (default = otlp_proto): The name of the built-in marshaler used to marshal metrics. See [Built-in Marshalers](#built-in-marshalers).
+  - `encoding_extension`: The name of the encoding extension used to marshal metrics. This configuration option is mutually exclusive with `marshaler`. See [Encoding extensions](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/extension/encoding/README.md).
+- `traces`
+  - `subject` (default = "otel_traces"): The [OTTL value expression](https://pkg.go.dev/text/template) used to construct NATS subjects for traces.
+  - `marshaler` (default = otlp_proto): The name of the built-in marshaler used to marshal traces. See [Built-in Marshalers](#built-in-marshalers).
+  - `encoding_extension`: The name of the encoding extension used to marshal traces. This configuration option is mutually exclusive with `marshaler`. See [Encoding extensions](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/extension/encoding/README.md).
+- `auth`
+  - `token`: Configuration options for [token auth](https://docs.nats.io/running-a-nats-service/configuration/securing_nats/auth_intro/tokens).
+    - `token`: The plaintext token.
+  - `user`: Configuration options for [username/password auth](https://docs.nats.io/running-a-nats-service/configuration/securing_nats/auth_intro/username_password).
+    - `username`: The plaintext username.
+    - `password`: The plaintext password.
+  - `nkey`: Configuration options for [NKey auth](https://docs.nats.io/running-a-nats-service/configuration/securing_nats/auth_intro/nkey_auth).
+    - `public_key`: The public key.
+    - `seed`: The seed.
+  - `nkey_jwt`: Configuration options for [decentralized NKey auth via JWT](https://docs.nats.io/running-a-nats-service/configuration/securing_nats/auth_intro/jwt).
+    - `jwt`: The JWT.
+    - `seed`: The seed.
+  - `nkey_user_file`: Configuration options for [decentralized NKey auth via user file](https://docs.nats.io/using-nats/developer/connecting/creds).
+    - `user_file`: The path to the user file.
+
+### Built-in marshalers
+
+NATS Core exporter has built-in marshalers for the following built-in encodings:
+
+- `otlp_proto`: Signals are encoded as OTLP Protobuf.
+- `otlp_json`: Signals are encoded as OTLP JSON.
+
+## Example Configurations
+
+### Dynamic subjects
+
+To support [subject-based filtering](https://docs.nats.io/nats-concepts/subjects#subject-based-filtering-and-security), NATS Core exporter constructs dynamic subjects using [OTTL value expressions](https://pkg.go.dev/text/template).
+
+Below is an example of dynamic subjects for traces:
+
+```yaml
+natscoreexporter:
+  traces:
+    subject: 'Format("traces.%s.spans.%s", [span.trace_id, span.span_id])'
+```