Make federation domain customizable

roles/matrix-base/defaults/main.yml

@@ -11,6 +11,9 @@ matrix_domain: ~
 # This and the Element FQN (see below) are expected to be on the same server.
 matrix_server_fqn_matrix: "matrix.{{ matrix_domain }}"
 
+# This is where you access federation API.
+matrix_server_fqn_matrix_federation: '{{ matrix_server_fqn_matrix }}'
+
 # This is where you access the Element web UI from (if enabled via matrix_client_element_enabled; enabled by default).
 # This and the Matrix FQN (see above) are expected to be on the same server.
 matrix_server_fqn_element: "element.{{ matrix_domain }}"

roles/matrix-base/templates/static-files/well-known/matrix-server.j2

@@ -1,4 +1,4 @@
 #jinja2: lstrip_blocks: "True"
 {
-	"m.server": "{{ matrix_server_fqn_matrix }}:{{ matrix_federation_public_port }}"
+	"m.server": "{{ matrix_server_fqn_matrix_federation }}:{{ matrix_federation_public_port }}"
 }