Major Description
The time name of `TimestampWithoutTZType` is verbose. Rename it as `TimestampNTZType` so that
1. it is easier to read and type.
2. As we have the function to_timestamp_ntz, this makes the names consistent.
3. We will introduce a new SQL configuration `spark.sql.timestampType` for the default timestamp type. The configuration values can be "TIMESTMAP_NTZ" or "TIMESTMAP_LTZ" for simplicity.
