feat(gen): add slack webhook

Author: SamyOubouaziz

.github/workflows/link-check-schedule.yml

@@ -20,6 +20,8 @@ jobs:
       if: always() # Triggers step if previous step fails. Must be added to consecutive steps as well.
       uses: slackapi/[email protected] # ref: https://github.com/slackapi/slack-github-action
       with:
+        payload: |
+          text: The link check results are available here.
         payload-file-path: "linkcheck_output.txt"
         webhook: ${{ secrets.SLACK_WEBHOOK_URL }}
         webhook-type: webhook-trigger