Enable metrics endpoint for mautrix bridges by default when Prometheus is enabled

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

This just enables the endpoint, which is somewhat helpful, but not
really enough to scrape them. Ideally, we'd be injecting these targets
into the Prometheus scrape config too.
For now, registering targets with Prometheus is very manual
(`matrix_prometheus_scraper_postgres_enabled`, `matrix_prometheus_scraper_hookshot_enabled`, ..).
This should be redone - e.g. a new `matrix_prometheus_scrape_config_jobs_auto` variable,
which is dynamically built in `group_vars/matrix_servers`.

group_vars/matrix_servers

@@ -807,6 +807,12 @@ matrix_mautrix_facebook_login_shared_secret: "{{ matrix_synapse_ext_password_pro
 
 matrix_mautrix_facebook_bridge_presence: "{{ matrix_synapse_presence_enabled if matrix_synapse_enabled else true }}"
 
+# People using an external Prometheus server will need to toggle all of these to be able to consume metrics remotely:
+# - `matrix_mautrix_facebook_metrics_enabled`
+# - `matrix_mautrix_facebook_proxying_metrics_enabled`
+# - `matrix_nginx_proxy_proxy_matrix_metrics_enabled`
+matrix_mautrix_facebook_metrics_enabled: "{{ matrix_prometheus_enabled }}"
+
 # We'd like to force-set people with external Postgres to SQLite, so the bridge role can complain
 # and point them to a migration path.
 matrix_mautrix_facebook_database_engine: "{{ 'postgres' if devture_postgres_enabled else 'sqlite' }}"
@@ -934,6 +940,12 @@ matrix_mautrix_instagram_login_shared_secret: "{{ matrix_synapse_ext_password_pr
 
 matrix_mautrix_instagram_bridge_presence: "{{ matrix_synapse_presence_enabled if matrix_synapse_enabled else true }}"
 
+# People using an external Prometheus server will need to toggle all of these to be able to consume metrics remotely:
+# - `matrix_mautrix_instagram_metrics_enabled`
+# - `matrix_mautrix_instagram_proxying_metrics_enabled`
+# - `matrix_nginx_proxy_proxy_matrix_metrics_enabled`
+matrix_mautrix_instagram_metrics_enabled: "{{ matrix_prometheus_enabled }}"
+
 # We'd like to force-set people with external Postgres to SQLite, so the bridge role can complain
 # and point them to a migration path.
 matrix_mautrix_instagram_database_engine: "{{ 'postgres' if devture_postgres_enabled else 'sqlite' }}"
@@ -979,6 +991,12 @@ matrix_mautrix_signal_appservice_token: "{{ '%s' | format(matrix_homeserver_gene
 
 matrix_mautrix_signal_login_shared_secret: "{{ matrix_synapse_ext_password_provider_shared_secret_auth_shared_secret if matrix_synapse_ext_password_provider_shared_secret_auth_enabled else '' }}"
 
+# People using an external Prometheus server will need to toggle all of these to be able to consume metrics remotely:
+# - `matrix_mautrix_signal_metrics_enabled`
+# - `matrix_mautrix_signal_proxying_metrics_enabled`
+# - `matrix_nginx_proxy_proxy_matrix_metrics_enabled`
+matrix_mautrix_signal_metrics_enabled: "{{ matrix_prometheus_enabled }}"
+
 matrix_mautrix_signal_database_engine: 'postgres'
 matrix_mautrix_signal_database_hostname: "{{ devture_postgres_connection_hostname if devture_postgres_enabled else '' }}"
 matrix_mautrix_signal_database_password: "{{ '%s' | format(matrix_homeserver_generic_secret_key) | password_hash('sha512', 'mau.signal.db', rounds=655555) | to_uuid }}"
@@ -1103,6 +1121,12 @@ matrix_mautrix_whatsapp_homeserver_token: "{{ '%s' | format(matrix_homeserver_ge
 
 matrix_mautrix_whatsapp_login_shared_secret: "{{ matrix_synapse_ext_password_provider_shared_secret_auth_shared_secret if matrix_synapse_ext_password_provider_shared_secret_auth_enabled else '' }}"
 
+# People using an external Prometheus server will need to toggle all of these to be able to consume metrics remotely:
+# - `matrix_mautrix_twitter_metrics_enabled`
+# - `matrix_mautrix_twitter_proxying_metrics_enabled`
+# - `matrix_nginx_proxy_proxy_matrix_metrics_enabled`
+matrix_mautrix_twitter_metrics_enabled: "{{ matrix_prometheus_enabled }}"
+
 # Postgres is the default, except if not using internal Postgres server
 matrix_mautrix_whatsapp_database_engine: "{{ 'postgres' if devture_postgres_enabled else 'sqlite' }}"
 matrix_mautrix_whatsapp_database_hostname: "{{ devture_postgres_connection_hostname if devture_postgres_enabled else '' }}"