Add support for CREATE ... SPLIT INTO when target database is YugabyteDB

[ssherwood]

YugabyteDB supports additional syntax for splitting tables into multiple tablets upon creation.

It would be beneficial for this syntax be an optional parameter when the target database is YugabyteDB - particularly when it is know that the source table has a large number of existing rows. The RF factor of the target database should be used to help calculate the number of splits.

This will help when loading large datasets as the built-in auto tablet splitting won't have to do as much work during the load itself.