ENH Provide hook for updating absoluteBaseURL

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

@@ -460,12 +460,14 @@ public static function absoluteURL($url, $relativeParent = self::BASE)
         if ($relativeParent === self::ROOT || self::is_root_relative_url($url)) {
             // Root relative urls always should be evaluated relative to the root
             $parent = self::protocolAndHost();
+            static::singleton()->extend('updateAbsoluteBaseURL', $parent);
         } elseif ($relativeParent === self::REQUEST) {
             // Request relative urls rely on the REQUEST_URI param (old default behaviour)
             if (!isset($_SERVER['REQUEST_URI'])) {
                 return false;
             }
             $parent = dirname($_SERVER['REQUEST_URI'] . 'x');
+            static::singleton()->extend('updateAbsoluteBaseURL', $parent);
         } else {
             // Default to respecting site base_url
             $parent = self::absoluteBaseURL();
@@ -932,10 +934,12 @@ public static function fileExists($file)
      */
     public static function absoluteBaseURL()
     {
-        return self::absoluteURL(
+        $absolute = self::absoluteURL(
             self::baseURL(),
             self::ROOT
         );
+        static::singleton()->extend('updateAbsoluteBaseURL', $absolute);
+        return $absolute;
     }
 
     /**