Cache merge requests count in group pages sidebar
Related to #243753 (closed)
Similar to the implementation for issues, we could save page load time for all pages at a group level, by caching the merge requests count in the sidebar.
The query for this count is performed in GroupsHelper#group_merge_requests_count and called from the sidebar partial.
At the date this issue was created, and for GitLab.org group, this query takes ~50ms.
To be determined:
- Do we also want to cache and round this count only after a certain value?