Add Slack announcement to nginxcommunity (#292)

This will send a message to the `#announcements` channel on release.

Author: lucacome

.github/workflows/ci.yml

@@ -126,6 +126,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           GOPATH: ${{ steps.go.outputs.go_path }}
           HOMEBREW_TAP_GITHUB_TOKEN: ${{ secrets.NGINX_PAT }}
+          SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK_COMMUNITY }}
       - name: Push to Dockerhub
         uses: docker/build-push-action@v3
         with:

.goreleaser.yml

@@ -62,3 +62,9 @@ brews:
     commit_author:
       name: nginx-bot
       email: [email protected]
+
+announce:
+  slack:
+    enabled: true
+    channel: '#announcements'
+    message_template: 'NGINX Prometheus Exporter {{ .Tag }} is out! Check it out: {{ .ReleaseURL }}'