Use |to_json in mautrix metrics configuration

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2427

roles/custom/matrix-bridge-mautrix-facebook/templates/config.yaml.j2

@@ -62,7 +62,7 @@ appservice:
 
 # Prometheus telemetry config. Requires prometheus-client to be installed.
 metrics:
-    enabled: {{ matrix_mautrix_facebook_metrics_enabled }}
+    enabled: {{ matrix_mautrix_facebook_metrics_enabled | to_json }}
     listen_port: 8000
 
 # Bridge config

roles/custom/matrix-bridge-mautrix-instagram/templates/config.yaml.j2

@@ -57,7 +57,7 @@ appservice:
 
 # Prometheus telemetry config. Requires prometheus-client to be installed.
 metrics:
-  enabled: {{ matrix_mautrix_instagram_metrics_enabled }}
+  enabled: {{ matrix_mautrix_instagram_metrics_enabled | to_json }}
   listen_port: 8000
 
 instagram:

roles/custom/matrix-bridge-mautrix-signal/templates/config.yaml.j2

@@ -67,7 +67,7 @@ appservice:
 
 # Prometheus telemetry config. Requires prometheus-client to be installed.
 metrics:
-    enabled: {{ matrix_mautrix_signal_metrics_enabled }}
+    enabled: {{ matrix_mautrix_signal_metrics_enabled | to_json }}
     listen_port: 8000
 
 # Manhole config.

roles/custom/matrix-bridge-mautrix-twitter/templates/config.yaml.j2

@@ -65,7 +65,7 @@ appservice:
 
 # Prometheus telemetry config. Requires prometheus-client to be installed.
 metrics:
-    enabled: {{ matrix_mautrix_twitter_metrics_enabled }}
+    enabled: {{ matrix_mautrix_twitter_metrics_enabled | to_json }}
     listen_port: 8000
 
 # Bridge config

roles/custom/matrix-bridge-mautrix-whatsapp/templates/config.yaml.j2

@@ -67,7 +67,7 @@ segment_key: null
 # Prometheus config.
 metrics:
     # Enable prometheus metrics?
-    enabled: {{ matrix_mautrix_whatsapp_metrics_enabled }}
+    enabled: {{ matrix_mautrix_whatsapp_metrics_enabled | to_json }}
     # IP and port where the metrics listener should be. The path is always /metrics
     listen: 0.0.0.0:8001