Create a script that stops the possibility of re-adding old release notes

As a developer I would like to reduce/stop the possibility of re-adding old release notes to releasenotes_upcoming.md - currently after we do a release the release notes upcoming is cleared of release notes which causes merge conflicts to PRs that existed beforehand. This ticket is to create a simple script which rebases to the current master/main and therefore stops the merge conflict.

### Acceptance Criteria
- [ ] Script is written that does the above
- [ ] We add this script to one of the post-release steps on the wiki