Add packit support

[germag]

Let's add support for packit so we can run our test on each PR

[lmilbaum]

Can you please clarify how packit can help with running our tests?

[ckyrouac]

copying a comment from @henrywang from a separate thread:

I think containers org already onboarded Packit. Packit will be a good choice for podman-bootc test. Packit does not consume github action runner and it's well integrated with testing farm and tmt. Packit does not need testing farm API token either. In this podman-bootc case, secret is not required and the only requirement should be nested virtualization. Testing farm can be configured to request a nested virtualization runner for both x86_64 and aarch64. So we should use Packit.