Add top/host level configuration for airgap

[kke]

Instead of using the files: feature, it would work like the k0s binary uploads.

spec:
  hosts:
    - role: controller
      airgap: true

spec:
  hosts:
    - role: controller
      airgapBundlePath: files/k0s-airgap-bundle-x86-1.23+k0s.4 # similar to the k0sBinaryPath

This could also have a feature that would prepare your k0sctl host's caches, something like k0sctl prepare-airgap which would download all the required binaries + bundles to local cache, then you can take your machine to the bunker and run apply there. Maybe with something like --output-directory /mnt/usb_stick/k0s_binaries.