[Request]: User-specified mounts in machines.

### Feature or enhancement request details

Thanks for the new `container machine`, I've been playing with it tonight and it's really great 👏

Whilst I can see there's a `--home-mount` flag, I haven't found a way to mount additional arbitrary paths from my Mac into the machine. It would be super useful if there was something along the lines of `--mount /Volumes/Project:/Project` that worked a similar manner to `--volume` for containers.

Keep up the great work, it's so nice having a first-party tool for all of this.

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Start at the `container machine` CLI entry point and inspect how the existing `--home-mount` option is handled. Compare its behavior with container `--volume` handling, then determine what is needed for an additional `--mount` option accepting arbitrary Mac paths; done means those paths are available inside the machine.

Written by the indexing model from the issue text.