Add `OutlierDetectingEndointGroup`

[ikhoon]

Currently, a CircuitBreaker cannot be applied individually to each endpoint in an EndpointGroup. OutlierDetectingEndointGroup internally uses CircuitBreaker to collect request results and avoid sending requests to bad Endpoints.

• If a request to an Endpoint does not receive 2xx-4xx status, the CircuitBreaker increases the failure count for the Endpoint.
• If the failure count exceeds the threshold defined in a CircuitBreaker option, the Endpoint is removed from the valid Endpoints and a new [Endpoint] will be added if available.

[hyunw9]

If no one is currently assigned to this task and it hasn't been implemented yet, would it be alright if I take care this issue?

[ikhoon]

Thanks for your interest. However, I've already implemented OutlierDetectingEndointGroup internally and plan to publish it after redesigning its public API.

[hyunw9]

I see, and thank you for letting me know.