Add support for not serving Dendrite federation APIs on the client port

Seems like Dendrite encourages serving both the Client and Federation
API at the same port.

Coming from Synapse and how things are done there, we have separate
ports. Using separate ports probably makes matrix-corporal (etc.)
integration easier, so separating the APIs by default probably makes
sense.

roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-dendrite.conf.j2

@@ -14,6 +14,16 @@ server {
 		{{- configuration_block }}
 	{% endfor %}
 
+	{% if matrix_nginx_proxy_proxy_dendrite_block_federation_api_on_client_port %}
+	location /_matrix/federation {
+		{% if matrix_nginx_proxy_proxy_dendrite_federation_api_enabled %}
+			return 404 'The Federation API is served at https://{{ matrix_server_fqn_matrix }}:{{ matrix_federation_public_port }}';
+		{% else %}
+			return 404 'This Matrix server is running with federation disabled';
+		{% endif %}
+	}
+	{% endif %}
+
 	{# Everything else just goes to the API server ##}
 	location / {
 		{% if matrix_nginx_proxy_enabled %}