* Refactor agent supervisor listener startup and authn/authz to use upstream
auth delegators to perform for SubjectAccessReview for access to
metrics.
* Convert spegel and pprof handlers over to new structure.
* Promote bind-address to agent flag to allow setting supervisor bind
address for both agent and server.
* Promote enable-pprof to agent flag to allow profiling agents. Access
to the pprof endpoint now requires client cert auth, similar to the
spegel registry api endpoint.
* Add prometheus metrics handler.
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>