KAFKA-20132: Implement TimestampedKeyValueStoreWithHeaders (1/N) (apache#21444)

This PR extracts the `DualColumnFamilyAccessor` from
`RocksDBTimestampedStore` and generalizes it so it can be used by both
`RocksDBTimestampedStore` and headers-aware stores. It also adds
corresponding unit tests.

Reviewers: TengYao Chi <frankvicky@apache.org>, Matthias J. Sax
 <matthias@confluent.io>

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Co-authored-by: TengYao Chi <kitingiao@gmail.com>

Author: aliehsaeedii