Support paginated response in GET-AzureRmMlWebService

[NonStatic2014]

Paginated response will happen when there are more than 1000 items returned back from the server. This is a corner case for current Azure Machine Learning users. So this change is for future-proof.

[cormacpayne]

@NonStatic2014 it looks like if this.ResourceGroupName isn't null, then these two methods will be called twice (once before the if-statement, and once inside. Is there a reason for doing this instead of doing the following:

if (this.ResourceGroupName != null)
{
     Func<Task<ResponseWithContinuation<WebService[]>>> getFirstServicesPageCall = () => this.WebServicesClient.GetAzureMlWebServicesBySubscriptionAsync(this.ResourceGroupName, null, this.CancellationToken);
     Func<string, Task<ResponseWithContinuation<WebService[]>>> getNextPageCall = nextLink => this.WebServicesClient.GetAzureMlWebServicesBySubscriptionAsync(this.ResourceGroupName, nextLink, this.CancellationToken);
}
else
{
     Func<Task<ResponseWithContinuation<WebService[]>>> getFirstServicesPageCall = () => this.WebServicesClient.GetAzureMlWebServicesBySubscriptionAsync(null, this.CancellationToken);
     Func<string, Task<ResponseWithContinuation<WebService[]>>> getNextPageCall = nextLink => this.WebServicesClient.GetAzureMlWebServicesBySubscriptionAsync(nextLink, this.CancellationToken);
}

[NonStatic2014]

I think it is the same thing, just an overwrite if this.ResourceGroupName is not null.

[cormacpayne]

LGTM