feat: users can have their own Git repo that will be persisted

Their '.git' and '.gitignore' are renamed before the commit/push on the Gitea repo so that they can be staged. After the push they are renamed back to '.git' and '.gitignore'. If a repository already exists, when the code is pulled at the start, the user's git files will also be renamed back.

MR de feat-git-student vers fix-commit-any-challenge-type pour le diff