Keep repositories synchronized option when forking repos
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=339042)
</details>
<!--IssueSummary end-->
### Proposal
Our [current option](https://about.gitlab.com/blog/2016/12/01/how-to-keep-your-fork-up-to-date-with-its-origin/) to keep repositories in sync requires configuration, and might not be scalable, since it requires user credentials to perform the repository mirroring.
Would it be possible to offer a system-level sync, as [bitbucket does](https://confluence.atlassian.com/bitbucketserver/keeping-forks-synchronized-776639961.html)?
issue