Endpoint Dial Metrics

[smilindave26]

(maybe this should be in the C SDK?)

It would be useful to collect metrics per service of Dial attempt successes and failures, so apps like ZDE and ZME can present in their UI to help indicate service help.

The macOS ZDE, for example, shows a service as "green" if the connection to the controller and posture checks are passing. To know if the service is really working (or occasionally working), we need to know if attempts to access the service succeed or fail.