This PR can be split into two parts:
* controllers
* apid binding into COSI world
Controllers
-----------
* `k8s.EndpointController` provides control plane endpoints on worker
nodes (it isn't required for now on control plane nodes)
* `secrets.RootController` now provides OS top-level secrets (CA cert)
and secret configuration
* `secrets.APIController` generates API secrets (certificates) in a bit
different way for workers and control plane nodes: controlplane nodes
generate directly, while workers reach out to `trustd` on control plane
nodes via `k8s.Endpoint` resource
apid Binding
------------
Resource `secrets.API` provides binding to protobuf by converting
itself back and forth to protobuf spec.
apid no longer receives machine configuration, instead it receives
gRPC-backed socket to access Resource API. apid watches `secrets.API`
resource, fetches certs and CA from it and uses that in its TLS
configuration.
Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>
