feat: disable federation

Closes https://git.coopcloud.tech/coop-cloud/matrix-synapse/issues/19.

homeserver.yaml.tmpl

@@ -310,9 +310,15 @@ listeners:
     type: http
     x_forwarded: true
 
+    {{ if eq (env "DISABLE_FEDERATION") "1" }}
+    resources:
+      - names: [client]
+        compress: false
+    {{ else }}
     resources:
       - names: [client, federation]
         compress: false
+    {{ end }}
 
     # example additional_resources:
     #
@@ -649,6 +655,9 @@ retention:
 #  - lon.example.com
 #  - nyc.example.com
 #  - syd.example.com
+{{ if eq (env "DISABLE_FEDERATION") "1" }}
+federation_domain_whitelist: []
+{{ end }}
 
 # Report prometheus metrics on the age of PDUs being sent to and received from
 # the following domains. This can be used to give an idea of "delay" on inbound