ci: Rework the integration tests to be reusable

[cdecker]

Just an experiment really. I was wondering how we could make the integration testing script more readable and make some components more approachable. For example we have dozens of places we compile and test with a variety of difference configurations, so pulling that into a reusable flow can remove some of the complexity. Reusable flows also seem much simpler to maintain.

Anyway, just a test, give me a :+1: or :-1: if you like/dislike the idea.