Project dashboards call Gitlab::Git::Repository#ref_names which is slow
When loading a project dashboard it seems that
Gitlab::Git::Repository#ref_names is called at least once for every request. While running
siege -i -c 4 -t 30m 'https://gitlab.com/gitlab-org/gitlab-ce' the timings for this method are as follows:
We should investigate if it's possible to cache the output of this method (or whatever final output is built using this method) so we don't end up hitting Git on every request.