ENH Provide hook for updating the parent used for absoluteURL

One use case for this that I've run into a few times is for sending emails using a queued job from the CLI.

src/Control/Director.php

@@ -470,6 +470,7 @@ public static function absoluteURL($url, $relativeParent = self::BASE)
             // Default to respecting site base_url
             $parent = self::absoluteBaseURL();
         }
+        static::singleton()->extend('updateAbsoluteURLParent', $parent);
 
         // Map empty urls to relative slash and join to base
         if (empty($url) || $url === '.' || $url === './') {