plugin architecture: custom rules/policy/scripts/config/etc.

[mmguero]

@mmguero cloned issue idaholab/Malcolm#581 on 2024-10-01:

This is a sub-issue of Malcolm "plugin architecture" #399

One type of plugin could contain custom rules, policy, or configuration. Basically anything covered in "policy manager" for Malcolm and Hedgehog Linux (there is some overlap between that feature and this one)

Also, I want to include everything talked about in Custom Rules, Scripts, and Plugins here in this issue. Anything that the user could create by dropping the files described in that documentation into a plugin ought to be handled as well.