Adding circleci (initial)

[nabadger]

Nearly there.

This gives us:

• helm linting
• generated template validation
• validation that the helm charts install to minikube (or similar)
• validation that the container can be built, and run (i.e. the go code compiles and doesn't crash on startup).

We can start building more tests as required (for now I just want to make sure the 2 components can talk to eachother).

initial todo:

• make dex-k8s-auth chart use a an image built from CI
• use a values-override file for helm (at least for dex-k8s-auth)