Add LUKS support

[edeckers]

I've added LUKS support (edeckers/csi-digitalocean) to release 1.2.0 by merging code from cloudscale-ch/csi-cloudscale.

It has been working very well for me, since I started using it about a week ago on DO managed Kubernetes.

Would you like me to create a PR for this?

[timoreimann]

hey there @edeckers 👋

we'd absolutely appreciate a patch to get LUKS support into our driver. 🎉 Happy to review any PRs of yours.