FR: search commit by SHA in all repositories

Problem to solve

Allow user to find commit in Git repositories, when user knows hash (SHA) of target commit, like 448c19a (e.g. from error message in deployed software), but doesn't know in which repositories to look for it.

Proposal

Implement a search by commit hash in Git repositories that are available to the user for reading. User should be able to search by both short (like 448c19a) and full (like 448c19aab1689ef43658a1f0fa0315e206ae895f) hash form.

Reference

This FR is akin to #442009 FR.

This FR is similar to gitlab-foss#24833 (closed), which was closed via merge request 7 years ago, but not implemented for now.