ESQL query builder prototype

[miguelgrinberg]

This PR contains a prototype of an ES|QL query builder feature for the PHP client based on the one I built for the Python client.

Example usage:

$query = Esql\Query::from("books", "books*")
    ->where('author == "King"', 'year == 1982')
    ->limit(10);
echo $query;

Output:

FROM books, books*
| WHERE author == "King" AND year == 1982
| LIMIT 10

In IDEs, you get correct suggestions based on context. For example:

[ezimuel]

@miguelgrinberg thanks for the PR it looks interesting. The only comment that I've at the moment is to split each class in a separate file. The name of the file must be the same of the class. This is a best practices in PHP .

[miguelgrinberg]

@ezimuel I refactored into multiple files (one per class) and added a couple more commands now. Let me know if this structure seems reasonable and I'll add the remaining commands and all the docs.

Two usage examples:

use Elastic\Elasticsearch\Helper\Esql;

$query = Esql\Query::from("books", "books*")
    ->where('author == "King"', 'year == 1982')
    ->limit(10);
echo $query;

$query = Esql\Query::row(a: 123, b: "test")
    ->limit(1);
echo $query;