Most of the groundwork was laid in previous PRs between adding the cert-monitor package to extracting the logic of signing certificates out of the connect_ca_endpoint.go code and into a method on the server.
This also refactors the auto-config package a bit to split things out into multiple files.
This is instead of having the AutoConfigBackend interface provide functions for retrieving them.
NOTE: the config is not reloadable. For now this is fine as we don’t look at any reloadable fields. If that changes then we should provide a way to make it reloadable.
