Expand disk image size after creation

Currently we cannot expand a disk that has already been initialized (with the OS installed). This would be helpful especially during MacOS upgrades as it sometimes needs to take up a lot of space.

No files, tests, or entry points are named in the issue. Start by locating the code responsible for creating and managing initialized disk images, then determine how expansion should work for existing images. Done means an initialized disk can be expanded after creation, including for macOS upgrade space needs.

Written by the indexing model from the issue text.