Currently the gRPC server assumes that if you have configured TLS certs
on the agent (for RPC) that you want gRPC to be encrypted. If gRPC is
bound to localhost this can be overkill. For the API we let the user
choose to offer HTTP or HTTPS API endpoints independently of the TLS
cert configuration for a similar reason.

This setting will let someone encrypt RPC traffic with TLS but avoid
encrypting local gRPC traffic if that is what they want to do.