Allow plugins to define overlay commands that run inside of the overlay chroot. If the user adds an `override-overlay`, they can replace those commands, or they can wrap them and let `craftctl default` signal where the plugin's original commands would run. Unlike other steps, only `craftctl default` is accepted in `override-overlay`. This is not a regression because previously the `craftctl` command couldn't be used in an override-overlay scriptlet at all. In addition to `overlay-script` being mutually exclusive with `override-overlay`, `overlay-script` is now also mutually exclusive with the plugin offering overlay commands. - [ ] Have you followed the guidelines for contributing? - [ ] Have you signed the [CLA](http://www.ubuntu.com/legal/contributors/)? - [ ] Have you successfully run `make lint && make test`? - [ ] Have you added an entry to the changelog (`docs/reference/changelog.rst`)? --- CRAFT-5027