Make backoff delay configurable

Problem to solve

We are using GitLab mainly to manage our git repositories (no ci, no issues, ...). Historically if someone pushes to a repo, these changes should be available at some other host. We are using the Mirroring repositories feature, to push these changes (Community Edition).

If someone pushes "to fast" the backoff delay delays the push to the mirror (1 minute).

Proposal

The backoff delay should be configurable in seconds (one minute is still too long), ideally via the GitLab webinterface.

Links / references

https://gitlab.com/gitlab-org/gitlab-ee/issues/3832 https://gitlab.com/gitlab-org/gitlab-ee/commit/8eba4eb6262b1bd5565fd832eb56e01af006c885