[SPARK-3660][STREAMING] Initial RDD for updateStateByKey transformation

SPARK-3660 : Initial RDD for updateStateByKey transformation

I have added a sample StatefulNetworkWordCountWithInitial inspired by StatefulNetworkWordCount.

Please let me know if any changes are required.
I know this was existing code, but could you make this condition simpler 

`val headOption = if (itr.hasNext) Some(itr.next()) else None`

Thanks :)