Improve airgap workflow

[kravciak]

Description

Airgap workflow is currently cumbersome, this is an attempt to improve it

This combines 4 scripts for saving & loading images and policies into one. Also adding defaults for parameters that can be guessed from other files.

[viccuad]

Just as a heads up, given that it will change the workflow, this PR should come together with one that updates the docs (analogous to https://github.com/kubewarden/docs/pull/150) and one that updates the blogpost (analogous to https://github.com/kubewarden/kubewarden.io/pull/153).

[flavio]

Closing, we will revisit that later as discussed with @kravciak