Add --vitest flag

[NullVoxPopuli]

Uses https://github.com/NullVoxPopuli/vitest-blueprint

This is for projects where they don't need a test app or maybe have node things to test outside of the test app.

Ember historically hasn't made a decision on node-testing convention, but I think this is pretty easy (no other node testing tool comes close to the ease of use here (at least that's been released in 3+ months ago)).

For example, @ember/string's v2-addon-conversion PR the ember app has been fully removed in favor of node-only tests (which vitest is good at (minimal config, works with ESM and TS out of the box))).
This is because the addon is really just a utility library with some functions and doesn't do anything ember-specific.
So v2 addons become a blueprint for rollup libraries, and not anything just ember specific.

[NullVoxPopuli]

should we do this same technique for the app as well?
it would allow us to add ember-cli-typescript for TS porjects.

[ef4]

I think it's good that the blueprint you've made can compose after the addon blueprint so easily, and since it can I don't think it's worth adding to the API surface area of the our blueprint.

An alternative suggestion would be to create a general purpose hook that lets people shell out to their own arbitrary extra command at this place in the blueprint (avoiding the need for multiple NPM installs).