Performance problems with requests to /api/v3/repos/:owner/:repository/branches

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Issue

Impacted version: 4.39.0

Deployment mode: tomcat
Requests to /api/v3/repos/:owner/:repository/branches are very slow for repositories that have stale branches.
Those are branches with many commits behind master (thousands).

The problem is also visible in the loading of the branch view of a repo.

I think I tracked it down to the problem that loading the branches also walks through commits to find the number if diverging commits.

This takes 10s of seconds for our repo. This also results in Jenkins repo scan for new branches and tags failing with a timeout.

A solution probably needs to either make the rev walking faster or at least don't do it for the API request.