Sanitize meta query

[MARQAS]

Description of the Change

This PR uses the WP Core sanitize_query method to sanitize the meta_query to resolve the [bool] query does not support [must] issue

Closes #3226

How to test the Change

• Install Debug bar and Debug Bar ElasticPress
• Enable the query logging in the EP settings.
• Add a meta query with an integer key and see that the query does not show the error in the debug bar.
• Example query:

new WP_Query(
		array(
			'posts_per_page' => 5,
			'no_found_rows' => true,
			'post_status' => 'publish',
			'meta_query' => array( 0 => array() ),
			'ep_integrate' => true,

		)
	);

Changelog Entry

Fixed - Sanitization of Meta Query

Credits

Props @MARQAS

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[felipeelia]

@MARQAS Can we please add a unit test here to be sure this bug isn't reintroduced?