Create CLI tool

Having a `drifter` CLI tool would simplify the management of Drifter projects. It could for example:

* Install Drifter on a project by using `drifter install` instead of a `curl | sh`, and have an interactive process to set which box to use, and enable initial roles and set parameters
* Get the currently installed Drifter version on a project
* Upgrade Drifter on a project
* Any other idea?

The issue names no files, tests, or entry points. Start by reviewing the existing curl | sh installation flow and defining the scope of the proposed drifter install, version, and upgrade commands. Done should include an agreed command interface and working behavior for installation, version reporting, and upgrades.

Written by the indexing model from the issue text.