Integrate terraform-libvirt-provider support virtual machine provisioning

[rgielen]

This pull request adds support for provisioning hobbykube clusters based on KVM / QEMU virtual machines, utilizing terraform-libvirt-provider.

The module is fully functional, reasonably configurable and comes with documentation and example configuration placed in the module directory.

Hopefully others fid it useful.
Feedback is of course highly welcome.

[rgielen]

First finding: documentation lacks information that libvirt must be present on the provisioning machine, along with instructions how to set this up on Linux / MacOS

[pstadler]

I never said thank you for opening this pull request and I'm sorry about that, because you definitely put a lot of work into it. Unfortunately I have no setup to test this. As many people simply leave for good after submitting a PR, I'm wondering whether you'd want to create a repository with this module yourself and I'd put a section in the README here. What do you think?

[rgielen]

No worries, I know that keeping up with PRs can be very challenging, as is keeping PR branches up to date with origin master.
To further discuss how to deal with this PR, I'd need to rebase and verify it again, which I'm supposed to do as soon as time permits. I'm using this feature regularly, as it allows me to trade a Rasberry Pi cluster for a NUC+i9 when setting up multi node test clusters.
I'd also like to describe the setup of a minimal test system (Linux host with KVM/QEMU support) in the docs. Basically it should work not only with a bare metal Linux box, but also with VMWare, VirtualBox, MultiPass or even WSL2.
Once I've done my homework, I'll check back to further discuss wether this could be valuable for the original project, if you're ok with this.