[Event Hubs] Investigate Retry surface area

[conniey]

• The Retry policy has an interesting API surface area. From feedback: Track 2: Event Hubs Client Library #3655 (comment)

  class Retry {
     public Duration getNextRetryInterval(Exception lastException, Duration remainingTime);
  }

[conniey]

Move the concern of "lastException" into the consuming class, change int baseWaitTimeSeconds to a Duration.

[conniey]

Resolved by #4262