executors: Build ignite VM image outside of packer

Created by: eseliger

This PR extracts the process of building and importing the VM image for ignite. This in itself is not a huge improvement other than that the packer VMs don't have to do this all separately, but it will allow us to in the future release the artifacts of this separately. Good for use when using the binary, because customers don't need to reconstruct from our VM build process how this works.

Test plan

Verified on k8s that it still works correctly.