Use proxy url for homeserver CS API

roles/matrix-maubot/defaults/main.yml

@@ -15,7 +15,7 @@ matrix_maubot_management_hostname: "0.0.0.0"
 
 matrix_maubot_shared_secret: false
 matrix_maubot_registration_shared_secret:
-matrix_maubot_cs_url: http://matrix-synapse:8008
+matrix_maubot_cs_url: "{{ matrix_homeserver_container_url }}"
 matrix_maubot_admins: false
 
 matrix_maubot_docker_image: dock.mau.dev/maubot/maubot:latest