Add auto-dependabot.yaml workflow to repo-config and migrate script

[Marenz]

Instead of manually updating all repos with the auto-dependabot.yaml workflow, we should:

1. Add the auto-dependabot.yaml workflow to repo-config
2. Update the migrate script to:
   • Install/replace any existing workflow with the same name
   • Fix the ownership file (CODEOWNERS) as needed

Benefits

• Centralized management of the workflow
• Consistent deployment across all repos
• Automated updates via repo-config migrate script
• Can be tested in one repo before deploying everywhere

Current Status

Multiple PRs have been created manually to update existing workflows:

• 12 PRs currently open across frequenz repos
• 3 PRs already merged

Proposed Approach

1. Add the workflow template to repo-config with the correct format:

   - uses: frequenz-floss/dependabot-auto-approve@005e52004f5d5c6af2f81b89ec25e5cf6f3dfd77 # v1.3.0

2. Update migrate script to handle workflow installation/replacement
3. Update migrate script to fix CODEOWNERS if needed
4. Test in one repo first
5. Deploy via repo-config to all repos

Related

This would supersede the manual PR updates currently in progress.