synapse: add missing server_notices configuration variables

Add support for all server_notices settings documented by Synapse:
- room_avatar_url: optional avatar for the server notices room
- room_topic: optional topic for the server notices room
- auto_join: whether users are auto-joined instead of invited (default: false)

Signed-off-by: Norman Ziegner <n.ziegner@hzdr.de>

roles/custom/matrix-synapse/defaults/main.yml

@@ -1657,6 +1657,12 @@ matrix_synapse_server_notices_system_mxid_display_name: "Server Notices"
 matrix_synapse_server_notices_system_mxid_avatar_url: ~
 # The name of the room where server notices will be sent, this room will be created if it doesn't exist.
 matrix_synapse_server_notices_room_name: "Server Notices"
+# Optional avatar URL for the server notices room, example: mxc://example.com/abc123
+matrix_synapse_server_notices_room_avatar_url: ~
+# Optional topic for the server notices room.
+matrix_synapse_server_notices_room_topic: ~
+# If true, users will be automatically joined to the server notices room instead of being invited.
+matrix_synapse_server_notices_auto_join: false
 
 # Controls whether searching the public room list is enabled.
 matrix_synapse_enable_room_list_search: true

roles/custom/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -2730,6 +2730,13 @@ server_notices:
   system_mxid_avatar_url: {{ matrix_synapse_server_notices_system_mxid_avatar_url | string | to_json }}
 {% endif %}
   room_name: {{ matrix_synapse_server_notices_room_name | string | to_json }}
+{% if matrix_synapse_server_notices_room_avatar_url %}
+  room_avatar_url: {{ matrix_synapse_server_notices_room_avatar_url | string | to_json }}
+{% endif %}
+{% if matrix_synapse_server_notices_room_topic %}
+  room_topic: {{ matrix_synapse_server_notices_room_topic | string | to_json }}
+{% endif %}
+  auto_join: {{ matrix_synapse_server_notices_auto_join | to_json }}
 {% endif %}