Enable Docker Tests to Restart K3s service

[dereknola]

Is your feature request related to a problem? Please describe.
Currently, the k3s image produced by our build system only allows single execution of the k3s XXXX command on docker run or docker exec. This makes it impossible to test more complex scenarios such as Snapshot and Restore or Secrets Encryption or Cert Rotation.

Describe the solution you'd like
Use the systemd-node image instead of the k3s image to enable a "vm-lite" environment where k3s is run as a regular systemd service and can be stopped and restarted at will.

Describe alternatives you've considered

We already have vagrant VM tests to handle more complex clusters, but we are limited on how big those can get with the current GHA runners.

Additional context