Add the ability to create a makeshift Arch Linux repository in GitHub releases

[loathingKernel]

The goal of this PR is to add the necessary bits to generate the files (<reponame>.{db,db.tar.gz,files.file.tar.gz}) that constitute an Arch Linux repository.

The way it works is by updating the repository files and exposing them in the action outputs to be uploaded. It also allows for custom pacman and makepkg configuration files to pull dependencies from releases.

You can see it in use in my own repo here https://github.com/loathingKernel/PKGBUILDs

I am opening this as a draft to see if there is any interest in merging it and as a RFC. If this is something that could be included, I am will update the documentation too to reflect the changes.

The yay -> paru change or downloading it from alerque repository are not mandatory and I will exclude them from the final PR if they are not wanted.