Make nginx proxy config (when disabled) obey matrix_federation_public_port

People who were disabling matrix-nginx-proxy (in favor of their own
nginx webserver) and also overriding `matrix_federation_public_port`,
found that the generated nginx configuration still hardcoded `8448`,
which forced their nginx server to use that, regardless of the fact
that `matrix_federation_public_port` was pointing elsewhere.

We now allow for the in-container federation port to be configurable,
and also automatically wire things properly.

roles/matrix-nginx-proxy/defaults/main.yml

@@ -111,6 +111,10 @@ matrix_nginx_proxy_proxy_element_hostname: "{{ matrix_server_fqn_element }}"
 # Controls whether proxying the matrix domain should be done.
 matrix_nginx_proxy_proxy_matrix_enabled: false
 matrix_nginx_proxy_proxy_matrix_hostname: "{{ matrix_server_fqn_matrix }}"
+# The port name used for federation in the nginx configuration.
+# This is not necessarily the port that it's actually on,
+# as port-mapping happens (`-p ..`) for the `matrix-nginx-proxy` container.
+matrix_nginx_proxy_proxy_matrix_federation_port: 8448
 
 # Controls whether proxying the dimension domain should be done.
 matrix_nginx_proxy_proxy_dimension_enabled: false