chore: Tune release process (#947)

* Remove GH release when promoting to prod

This should now be done by release-please.

* Auto merge prod PR in deployment tools

Modifies the promote to production pipeline to auto merge the PR that is
performed to update the plugin in deployment tools, the same way it is
done for staging environment.

.drone.yml

@@ -212,7 +212,7 @@ steps:
     image: node:18
     commands:
       - ./scripts/install-ci-deps-apt.sh
-      - make install lint test build sign package gh-release
+      - make install lint test build sign package
     environment:
       GCP_KEY:
         from_secret: gcp_key
@@ -229,7 +229,7 @@ steps:
           "repo_owner": "grafana",
           "repo_name": "deployment_tools",
           "destination_branch": "master",
-          "pull_request_branch_prefix": "ci/synthetic-monitoring-plugin",
+          "pull_request_branch_prefix": "auto-merge/synthetic-monitoring-plugin",
           "pull_request_enabled": true,
           "pull_request_existing_strategy": "ignore",
           "pull_request_message": "Triggered by ${DRONE_COMMIT_LINK}. NOTE: prod does not refer directly to an environment it refers to stacks associated with the prod 'wave'. See [here](https://github.com/grafana/deployment_tools/blob/master/ksonnet/environments/hosted-grafana/waves/provisioned-plugins/README.md#waves) for more info.",