upgrade / reinstall pups

[tjstebbing]

We need a mechanism to both upgrade and reinstall pups with existing config

• a pup that has been uninstalled but not purged should be reinstallable
• a pup with newer versions should be upgradable

These are essentially the same thing from Dogebox's POV.

No migration mechanism:

This task should not consider implementing any migration tooling, that should be left to the pup itself. we should consider means by which a pup can inform the user about migrations that need to be done.