* 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>
(cherry picked from commit ff679fb3)
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>