This turns admitomatic into a self-standing service that can be used as
an admission controller.
I've tested this E2E on a local k3s server, and have some early test
code for that - but that'll land up in a follow up CR, as it first needs
to be cleaned up.
Change-Id: I46da0fc49f9d1a3a1a96700a36deb82e5057249b