After merging https://github.com/scylladb/scylladb/pull/17365, all backport labels should be added to PR (before we used to add backport labels to the issues).
Adding a GitHub action which will be triggered in the following conditions only:
1) The base branch is `master` or `next`
2) Pull request events:
- opened: For every new PR that someone opens, we will sync all labels from the linked issue (if available)
- labeled: This role only applies to labels with the `backport/` prefix. When we add a new label for the backport we will update the relevant issue or PR to get them both to sync
- unlabeled: Same as `labeled` only applies to the `backport/` prefix. When we remove a label for backport we will update the relevant issue or pr
Closesscylladb/scylladb#17715
ad76f0325e