Add filters to exclude post types

[gutobenn]

This PR adds two filters for disabling post types from triggering a purge.

In my case I am using it to exclude woocommerce orders:

add_filter( 'rt_nginx_helper_exclude_post_types', function( $post_types ) { $post_types[] = 'shop_order'; return $post_types; } );
add_filter( 'rt_nginx_helper_comment_change_exclude_post_types', function( $post_types ) { $post_types[] = 'shop_order'; return $post_types; } );