Make new meta fields searchable

[iamgabrielma]

The plugin introduces two new meta fields: _job_salary and _job_important_info , which are not searchable by default.

There seems to be a filter here: https://github.com/Automattic/WP-Job-Manager/blob/914f790050a7069a2bf7db9d5b91480d6bd256be/wp-job-manager-functions.php#L262 for:

			'_job_location',
			'_company_name',
			'_application',
			'_company_name',
			'_company_tagline',
			'_company_website',
			'_company_twitter',

That adds "join" and "where" queries for keywords. Something like the following could work:

function gma_wpjmef_new_searchable_meta_keys() {
    global $wpdb, $job_manager_keyword;
    $searchable_meta_keys[] = '_job_salary';
    $searchable_meta_keys[] = '_job_important_info';
    return $searchable_meta_keys;
}
add_filter('job_listing_searchable_meta_keys', 'gma_wpjmef_new_searchable_meta_keys');