[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.
nit: can you move this function the last version of `updateStateByKey` ? They are ordered from simplest to most complicated, and this one definitely the most complicated one.