feat(metrics): collect Headscale, NetBird, Gitea and Immich metrics

gitea/k8s/config.yaml

@@ -20,6 +20,8 @@ data:
 
   GITEA__mailer__ENABLED: "false"
 
+  GITEA__metrics__ENABLED: "true"
+
   # No code/issue search needed: bleve reindexes the whole issue index on
   # every pod restart (cron.rebuild_issue_indexer RUN_AT_START) and hammers
   # the rotational disk for an hour. "db" serves issue search from postgres.