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;

[miguelgrinberg]

@ezimuel This is ready to review!

Maybe what makes the most sense is for you to read the unit test file first, so that you see how all the commands are constructed.