Add $context to get_capability()

[felipeelia]

Description of the Change

Users wanting to manage synonyms-related capabilities, for example, can use the following snippet and add the manage_elasticpress_synonyms capability to their chosen role:

add_filter(
	'ep_capability',
	function ( $cacapability, $context ) {
		return ( 'synonyms' === $context ) ?
			'manage_elasticpress_synonyms' :
			$cacapability;
	},
	10,
	2
);

Closes #3787

How to test the Change

Changelog Entry

Added - Context parameter to the get_capability() function

Credits

Props @felipeelia @selim13

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.