[RFE] IONOS Cloud support

[tuunit]

Current situation

Currently no IONOS Cloud specific images exist.

Impact

It is not trivial or documented on how to use Flatcar in the IONOS Cloud. QEMU images start but Ignition or Cloud-Init user-data and sshkey injection are missing.

Ideal future situation

Simple build and deployment of IONOS Cloud compatible images.

Implementation parts

• [x] Ignition support: https://github.com/coreos/ignition/pull/1957
• [x] flatcar/scripts: https://github.com/flatcar/scripts/pull/2389
• [x] flatcar/init: https://github.com/flatcar/init/pull/127
• [x] flatcar/coreos-cloudinit: https://github.com/flatcar/coreos-cloudinit/pull/29
• [ ] Documentation: (open)
• ~Afterburn support: (open)~ (postponed until we have a proper metadata server)
• ~flatcar/bootengine: https://github.com/flatcar/bootengine/pull/100~ (no changes necessary)

Additional information

The IONOS Cloud as of yet doesn't have a metadata server. Therefore sshkeys and user-data is injected into the volume drive before a new Compute Engine / VM starts for the first time. The injection happens into the /var/lib/cloud/seed/nocloud/[user/meta]-data files.