Set file modification date to last relevant commit on git clone

[ableuler]

File metadata is not added to git. Therefore, after cloning a project, the file modification date will simply show the time/date of the clone. This can be confusing to users who would expect to see a file modification date similar to what's shown in the GitLab UI, which shows the date of the commit that last changed a file as file modification date. This project should allow us to do the same in our interactive environments. Alternatively, this could be a part of renku clone.