Decrease push mirror delay

Currently the soonest a change is push mirrored is at least 5 minutes after the change is detected. This is done for performance reasons to decrease the frequency of the push. In reality it is typically much slower.

This will also cause serious in bidirectional mirroring scenarios where delays will create more opportunity for conflict.

Proposal

• If Only mirror protected branches is true (https://gitlab.com/gitlab-org/gitlab-ee/issues/3843), push changes immediately
• Otherwise use existing slower logic

Links / references

Documentation blurb

Overview

What is it? Why should someone use this feature? What is the underlying (business) problem? How do you use this feature?

Use cases

Who is this for? Provide one or more use cases.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml