Add _timestamp_ms Virtual Column for Kafka Engine

Why it matters

This feature provides users with the ability to access the timestamp of Kafka messages with millisecond precision directly from the Kafka engine, enabling more precise time-based querying and processing of Kafka data.

How to use it

Users can simply query the Kafka engine and include the virtual column _timestamp_ms in their SELECT statements to retrieve the timestamp of each Kafka message with millisecond precision.