Add maintenance mode

[guettli]

/kind feature

Describe the solution you'd like

The cluster admin should have the option to get a machine into the maintenance mode.

If the controller detects that the cluster admin has set maintenance mode, then these steps should happen:

Steps

1. the machine gets drained
2. the machine gets deleted.
3. the machine gets provisioned with the default image.
4. The HivelocityMachine object gets deleted. But same hv-labels don't get removed. (See below)

Questions

How should the maintenance mode get triggered?

• setting a hv-label via hv-UI or hv-API
• via a boolean flag in the HivelocityMachine.
• Both.

The option "both" sound good, but we need to be sure that the controller can detect the change correctly.

Which labels get removed which should stay?

When a machine gets into maintenance mode these hv-labels should get removed:

These labels stay. I added example values, but of course it is about the key (the part before the equal sign)

• caphv-use=allow
• caphvlabel:deviceType=guettli-controlplane
• caphv-cluster-hv-guettli=owned
• caphv-cluster-name=hv-guettli
• caphv-permanent-error=...
• All other unknown labels should stay, too.

These labels will get removed:

• caphv-machine-name=hv-guettli-control-plane-5qkn4
• caphv-machine-type=control_plane