Add some early checks for missing basic requirements

[edwilde]

If the action is added to a repo without the proper files / config in place, then the error messaging is pretty cryptic when it fails.

This will happen if the repo is missing a phpunit config or phpcs config (and maybe php version in the composer.json, I am not sure).

It would be real nice if these super, obvious, basic things could be checked early on in the generate matrix task and display a helpful failure message.

Or maybe fail the task if the matrix is empty with some suggestions?

Making stuff Ed proof is good 🤡

[GuySartorelli]

Hi Ed,

That sounds like a good idea - but it'll be pretty low on the list of priorities right now. If you're willing to raise a PR adding these checks and dev-friendly messages we'd be happy to review it but otherwise it could be quite a while before this is prioritised.