Add string batchId overloads to CreateBatchOperation.Rehydrate methods

[KrzysztofCwalina]

This PR adds two new overloads to the CreateBatchOperation class for rehydrating batch operations directly from a batch ID string:

CreateBatchOperation.RehydrateAsync(BatchClient client, string batchId, CancellationToken cancellationToken = default)
CreateBatchOperation.Rehydrate(BatchClient client, string batchId, CancellationToken cancellationToken = default)