While working with an early access user, the usefulness of a command that
would be able to easily allow them to install all the plugins that we know
are necessary for migrating from a particular source platform was really clear.

It's analagous to dnf's concept of RPM groups, so I can pull everything I need
when I need a development toolchain, for example:

dnf groupinstall "Development Tools"

So in the crane world, what if I cuold run a command like:

```
crane plugin-manager groupinstall aks
crane plugin-manager groupinstall ocp
```

and I would get all the plugins that I need in order to go from aks to
ocp?

There are a lot of questions that come up when you start to think through what
this would entail based on our established model of plugin repositories.

Is the group a property that gets added to the metadata, and our pluginmanager
understands how to group them, and therefore install them?

Goal for this task is a proposed implementation for how to accomplish this
in the context of our current plugin model.