## What changes were proposed in this pull request?

**Description** from JIRA

The TimestampType in Spark SQL is of microsecond precision. Ideally, we should convert Spark SQL timestamp values into Parquet TIMESTAMP_MICROS. But unfortunately parquet-mr hasn't supported it yet.
For the read path, we should be able to read TIMESTAMP_MILLIS Parquet values and pad a 0 microsecond part to read values.
For the write path, currently we are writing timestamps as INT96, similar to Impala and Hive. One alternative is that, we can have a separate SQL option to let users be able to write Spark SQL timestamp values as TIMESTAMP_MILLIS. Of course, in this way the microsecond part will be truncated.
## How was this patch tested?

Added new tests in ParquetQuerySuite and ParquetIOSuite

Author: Dilip Biswal <dbiswal@us.ibm.com>

Closes #15332 from dilipbiswal/parquet-time-millis.