Add a SparkSessionExt createDS method

[MrPowers]

The createDF method is very useful.

I think a createDS method is needed as well, so we don't have to do this:

val sourceDS = spark.createDataset[Person](
  Seq(
    Person("Alice", 12),
    Person("Bob", 17)
  )
)

I'd rather do this:

val sourceDS = spark.createDS[Person](
  List(
    ("Alice", 12),
    ("Bob", 17)
  )
)

[MrPowers]

Meh, this looks like a nice to have & is not nearly as important as createDF