Add Mastodon API service class, auth token config

Add a new REST API service class to keep things DRY

app/models/concerns/settings/mastodon_settings.rb

@@ -11,6 +11,9 @@ module Settings
 
       field :mastodon_address_domain, type: :string,
         default: ENV["MASTODON_ADDRESS_DOMAIN"].presence || self.primary_domain
+
+      field :mastodon_auth_token, type: :string,
+        default: ENV["MASTODON_AUTH_TOKEN"].presence
     end
   end
 end