Update Gitlab::Git::HookEnv code comments
This adds a back-reference from the comments of Gitlab::Git::HookEnv to the new documentation at https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/object_quarantine.md#gitlab-and-git-object-quarantine.
Omitting all the checklists because this only changes code comments.
Edited by Jacob Vosmaer