Adds `volume` command and allows multiple disks

[sam-berning]

https://github.com/lima-vm/lima/issues/722

After looking through the discussion on https://github.com/lima-vm/lima/pull/759, I implemented a basic volume command. Volumes are stored under a _volumes directory under $LIMA_HOME and can be attached by name to an instance in its LimaYAML.

Also added a boot script that performs some setup for volumes. So far, it creates a filesystem labeled with the volume name if it's the first time the volume has been attached to an instance. In the future, we could expand it to bind-mount the volume to specific directories.

[jandubois]

Please fix linter errors (run make lint locally to verify).

[jandubois]

Please rebase the PR to resolve merge conflicts!

[AkihiroSuda]

Please squash commits and make sure to keep the PR title consistent with the actual code

[jandubois]

This PR also needs to be rebased on latest master so it can pass integration tests.