Alerting: Integration test for testing template via remote alertmanager (#92147)

* Add integration test for testing template

* Update drone signature

devenv/docker/blocks/mimir_backend/docker-compose.yaml

@@ -1,5 +1,5 @@
   mimir_backend:
-    image: grafana/mimir-alpine:r295-a23e559
+    image: grafana/mimir-alpine:r304-3872ccb
     container_name: mimir_backend
     command:
       - -target=backend
@@ -14,4 +14,4 @@
       - 8080:8080
     volumes:
       - "./docker/blocks/mimir_backend/nginx/nginx.conf.template:/etc/nginx/templates/nginx.conf.template"
-      - "./docker/blocks/mimir_backend/nginx/.htpasswd:/etc/nginx/.htpasswd"
+      - "./docker/blocks/mimir_backend/nginx/.htpasswd:/etc/nginx/.htpasswd"