[installer] Move `defaultBaseImageRegistryWhitelist` out of `experimental` section

[corneliusludmann]

We use defaultBaseImageRegistryWhitelist in production but it is part of the experimental section. We should move this out of experimental and replace all occurrences.

Proposal:

containerRegistry:
  # If you want to pull workspace base images from a private registry (with credentials), you need to make sure the credentials are available in containerRegistry.external.certificate and add this registry to privateBaseImageRegistries.
  privateBaseImageRegistries:
    - my-registry.example.com

I'm open to other naming proposals. However, I would like to avoid the term “whitelist”.

It is likely best to tackle this together with #11408

Value

• Tech-debt
• Allows the use of private base images

[lucasvaltl]

Related to #1699