Support raw_checksum for specified timestamp on APIv2

[Smityz]

Feature Request

Is your feature request related to a problem? Please describe:

It's a little bit difficult to check the integrity of the data when compose using BR and CDC,
because in real time replication, the data changes all the time. So, we can't use the original checksum function to validate data.

Describe the feature you'd like:

Support checksum for specified timestamp data.

Describe alternatives you've considered:

Don't know yet.

Teachability, Documentation, Adoption, Migration Strategy:

How about using coprocessor v2 to implement this function, avoiding changing proto define.