Agnostic_baker: Move shell code from plugin to agnostic baker

What

Parent MR: !16583 (merged)

Here we move the code that is not dependent on protocol from the plugin to the agnostic baker library.

Why

To simplify the agnostic baker plugin.

How

Manually testing the MR

Check the same way as was done in the parent MR, this MR should be a no-op (but rather a quality of life refactoring)

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR