Improvements to the air-gapped experience for KKP setups

[embik]

This is supposed to track improvements to the user experience when setting up air-gapped environments. While it works, we have received the feedback that it could be easier.

Tasks

Beta Give feedback

1. Allow mirror-images to create a bundle of images to import in air-gapped scenario #12368
   kind/feature +1
2. Provide single registry override for all images in a KKP setup #12465
   +0
3. Document package mirror requirements for air-gapped / offline mode docs#1493
   kind/documentation +1
4. Add Default Way to extend OSPs #12310
   customer-request kind/feature +2
5. Add feature for packaging and distributing binaries required for node bootstrapping #12467
   kind/feature +1