Feature: Expose internal site create/delete functions

[austinginder]

Need to expose internal functions of WP Freighter so other plugins can easily extend it's functionality. Maybe simplify the code base to handle site creation and deletion like so:

# Create new site
( new WPFreighter\Site )->create( [ "domain" => "captaincore.io", "title" => "CaptainCore", "username" => "admin", "email" => "[email protected]" ] );

# Delete a site
( new WPFreighter\Site )->delete( [ "site_id" => "2" ] );