This extends the archive creation logic to add annexed files to the
created archives. The basic flow is this:
1. Create an archive using `git archive`
2. Read in that archive and write out a new one, replacing all annexed
files with their annexed content; leaving the git-only files as-is
The file permissions with which the annexed files are put into the
archive are decided based on what `git archive` does for other files as
well:
- For tar.gz archives, executable files get permissions 0775 and regular
files get 0664.
- For zip archives, executable files get permissions 0755 and regular
files are archived with "FAT permissions" rw, instead of unix
permissions.
If for a given archive request an annexed file is not present on the
gitea instance then the content as tracked by git (i.e. a symlink or
pointer file) is silently put into the resulting archive instead.
Co-authored-by: Nick Guenther <nick.guenther@polymtl.ca>
