Enable begin and end cuts to be configurable

[adrdc]

Stream cuts mark positions in Pravega streams. When obtaining the segment ranges to iterate on in the Pravega connector, the segment manager expects a start and end stream cuts to mark the start and end positions in the stream to iterate over.

Currently, we set both to null, which means that we start at the first available position and ends at the current end of the stream. We should enable it to be configurable and let applications pass start and end stream cuts.