Add Exception to ApiCallAttempt metrics

If an SDK calls throws an exception (Http timeout, Resource not found exception), it would be useful to capture that as part of the `ApiCallAttempt` metrics collection.

Especially for an Http timeout, the SDK will make a bunch of attempts but for each attempt it will log only the `SigningDuration` and `BackoffDelayDuration` metric. If we want to investigate what happened to a particularly high latency call, looking at the detailed `ApiCallAttempt` metric would not give us the right hints. But having the Exception instance for each call attempt will be incredibly helpful.

Please consider adding an Exception metric record to the `ApiCallAttempt` metrics - this is currently done in the V1 SDK so should ideally be also made available to the V2 SDK.