Factor CLI abstractions out into module, for use by e.g., webUI

[squaremo]

The webUI will end up recapitulating many of the operations used by the CLI; for instance, fluxcd/webui#8.

It would be useful to separate those operations out into their own module, so they can be reused instead of duplicated. This will surely also help third-party integrations, e.g., further developments from eksctl-io/eksctl#3066.

[stefanprodan]

Relates to #291