feat: move allowed cors url to configuration file

- don't set cors origins form field as readonly and add deprecation notice.

installer/config.yml

@@ -6,6 +6,10 @@ general:
   # The internal API authentication key, this field is REQUIRED
   api_key:
 
+  # List of origins allowed to access resources on the server, default is []
+  # The public url origin is automatically included
+  allowed_cors_origins: []
+
   # How many hours ahead Playout should cache scheduled media files, default is 1
   cache_ahead_hours: 1