Configure Gitea Actions for Helm chart CI and release

- Replace GitHub chart-releaser with Gitea-compatible workflow
- Lint job: helm lint, template validation on push to main/master
- Release job: package and publish to Gitea releases on tag push (v*)
- Use gitea-release-action for creating releases
- Support both main and master branches

Co-authored-by: Cursor <cursoragent@cursor.com>

fleetdm-stack/templates/mysql-secret-alias.yaml

@@ -0,0 +1,11 @@
+# Fleet migration expects secret "mysql"; Fleet's MySQL subchart creates "fleetdm-stack-mysql".
+# This alias ensures the migration finds the password.
+apiVersion: v1
+kind: Secret
+metadata:
+  name: mysql
+  labels:
+    app.kubernetes.io/name: fleetdm-stack
+type: Opaque
+stringData:
+  mysql-password: {{ .Values.fleet.mysql.auth.password | quote }}