Remove requirement to run dummy IDP in same container as KMS

[DomAyre]

Currently the docker image under /docker/Dockerfile requires us to copy tests/utils/jwt because that's how we run a dummy IDP.

Because there is an implicit assumption that dummy IDP puts it certs in the same directory as the KMS workspace, we have to run both together, even though they're strictly different services.

I believe we have a more proper mechanism to trust a non-dummy IDP which doesn't have this assumption, so we should trust the dummy IDP with a similar interface, this would allow us to run the IDP independently in tests