DEV: Move discourse-chat to the core repo. (#18776)

As part of this move, we are also renaming `discourse-chat` to `chat`.

plugins/chat/app/controllers/api_controller.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class Chat::Api < Chat::ChatBaseController
+  before_action :ensure_logged_in
+  before_action :ensure_can_chat
+
+  private
+
+  def ensure_can_chat
+    raise Discourse::NotFound unless SiteSetting.chat_enabled
+    guardian.ensure_can_chat!(current_user)
+  end
+end