Replace BSTooltip with GlTooltip in mirror_repos.js

What does this MR do?

This Merge Request replaces the calls to Bootstrap’s jQuery tooltip API with a GitLab’s tooltip API implemented in #229044 (closed). This is part of the effort to replace Bootstrap’s javascript library with GitLab UI: &4383 (closed)

How to test?

You can open GitLab in the local environment and tooltips should keep working. For example, all tooltips in the dashboard should continue working correctly: