matrix: Autojoin new users to the #internal room

Now that login is restricted to staff members.

roles/matrix/templates/homeserver.yaml.j2

@@ -1350,6 +1350,7 @@ account_threepid_delegates:
 #
 auto_join_rooms:
   - "#archlinux:{{ matrix_server_name }}"
+  - "#internal:{{ matrix_server_name }}"
 
 # Where auto_join_rooms are specified, setting this flag ensures that the
 # the rooms exist by creating them when the first user on the