Add variable for appservice username template

roles/custom/matrix-bridge-rustpush/defaults/main.yml

@@ -151,6 +151,10 @@ matrix_rustpush_bridge_appservice_bot_username: imessagebot
 matrix_rustpush_bridge_appservice_bot_displayname: iMessage bridge bot
 matrix_rustpush_bridge_appservice_bot_avatar: ''
 
+# Localpart template for MXIDs of remote (iMessage) users.
+# The `{{.}}` placeholder expands to the iMessage handle (phone/email).
+matrix_rustpush_bridge_appservice_username_template: "{% raw %}imessage_{{.}}{% endraw %}"
+
 # Backfill is disabled by default because Linux Docker cannot access chat.db.
 # On macOS with Full Disk Access, this can be set to true.
 matrix_rustpush_bridge_backfill_enabled: false

roles/custom/matrix-bridge-rustpush/templates/config.yaml.j2

@@ -126,7 +126,7 @@ appservice:
     hs_token: {{ matrix_rustpush_bridge_homeserver_token | to_json }}
 
     # Localpart template of MXIDs for remote users.
-    username_template: "{% raw %}imessage_{{.}}{% endraw %}"
+    username_template: {{ matrix_rustpush_bridge_appservice_username_template | to_json }}
 
 # Config options that affect the Matrix connector of the bridge.
 matrix: