Add support for the aura helper

[willtrnr]

This is adding aura as a helper option.

However, this helper is a bit different. It works in reverse, meaning that it must be run as root and it drops privileges to run makepkg. This removes the need for the builder user and is pretty nice for Ansible use.

Also, it either uses only the AUR or only the repos for the requested packages (dependencies can be from both), there's no in between. Since this module is focused on AUR packages, I set it to use that (the -A flag instead of -S) and the aur_only option has no effect.

Feedback welcome if there's anything.

[kewlfft]

I am a bit skeptical with all the specificities you mention. Do you confirm your request is still relevant and is working with current aura version?

[willtrnr]

It's been quite a while, I personally no longer have the specific use-case I had for an AUR helper.
However, I guess it could be useful to some other users out there.
IMO, not having to create a builder user provides much better ergonomics in an Ansible context.

And, yes, this will still work on a current aura version.

[kewlfft]

It's adding some logic I won't have time to test, and you're not going to use it either. Thanks for the commit, I'll wait for one more user to express its interest here to add it.