ci: Add Archlinux

ci: Add Archlinux

Add an action to setup Archlinux and use it for the initial setup.
The rest of the workflow can stay the same.

Currently the Arch container in docker hub is not very up-to-date with
some expired keys and other keys not yet in the package. Workaround
that by wiping the current db and reinstalling the keyring. As requested
by Emil, add a comment in this part of the github-action about why
that is done.

Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>
Reviewed-by: Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/44