Support disabling bastion host

[simonklb]

/kind feature

Describe the solution you'd like

Currently, disabling a bastion host is not allowed after it has been enabled. Instead you have to tear down the entire cluster to remove it. I would like to be able to disable the bastion host while keeping the cluster alive.

Anything else you would like to add:

Support for enabling a bastion host was added in #1300. There it was decided that disabling the bastion once it had been enabled would not be allowed due to the lack of support for garbage collecting it. However a follow-up ticket was proposed to implement this in this Slack thread but I've not been able to find it when searching the issues here. Please close this as a duplicate if it already exist!

[dtzar]

This is not a duplicate, but this isn't on our priority list as you're the first person I know of to ask for it (aside from that slack request 3 years ago). PRs are welcome!