Add IAsyncEnumerable overload for GetAllReplicas

Motivation

The current GetAllReplicasAsync() API returns an IEnumerable<Task<IGetReplicaResult>> to the user, which is more difficult to use than if we were returning a "stream" of result using the IAsyncEnumerable interface (See LookupInAllReplicas and RangeScan).

Desired Outcome

Add a method to the ICouchbaseCollection interface or an extension method for GetAllReplicasAsync, which will return an IAsyncEnumerable<IGetReplicaResult>.