Send Brrr push notifications for new webmentions

Dispatches a queued job to POST to a configured Brrr webhook whenever
a brand-new webmention is saved, so replies/likes/reposts show up as
push notifications instead of requiring a manual check of the site.

config/services.php

@@ -39,4 +39,8 @@ return [
         'token' => env('CLOUDCONVERT_API_TOKEN'),
     ],
 
+    'brrr' => [
+        'webhook_url' => env('BRRR_WEBHOOK_URL'),
+    ],
+
 ];