ci: pass SLACK_RELEASES_WEBHOOK_URL to docker publish workflow

Wire the releases webhook secret so the docker publish end job can send
the Slack notification after images are pushed.

Author: AcevedoR

.github/workflows/release-docker.yml

@@ -32,4 +32,5 @@ jobs:
       DOCKERHUB_USERNAME: ${{ secrets.DOCKERHUB_USERNAME }}
       DOCKERHUB_PASSWORD: ${{ secrets.DOCKERHUB_PASSWORD }}
       SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+      SLACK_RELEASES_WEBHOOK_URL: ${{ secrets.SLACK_RELEASES_WEBHOOK_URL }}
       GH_PERSONAL_TOKEN: ${{ secrets.GH_PERSONAL_TOKEN }}