template metric toggle for mautrix bridges supporting it

roles/custom/matrix-bridge-mautrix-signal/defaults/main.yml

@@ -70,6 +70,9 @@ matrix_mautrix_signal_logging_level: WARNING
 # If false, created portal rooms will never be federated.
 matrix_mautrix_signal_federate_rooms: true
 
+# Whether or not metrics endpoint should be enabled.
+matrix_mautrix_signal_metrics_enabled: false
+
 # Database-related configuration fields
 #
 # This bridge only supports postgres.