Merge #41793

41793: ccl/changefeedccl: implement `WITH diff` option r=nvanbenschoten a=nvanbenschoten

Fixes #28666.

This commit adds a `WITH diff` option to CREATE CHANGEFEED. When the option is provided, changefeeds publications will include a `before` field, which includes the value of the row before the CDC update was applied.

We are able to implement this efficiently by pushing the option into Rangefeed and performing the scan of the previous value immediately before applying the update in the Raft processing goroutine. #41788 allows us to avoid performing this lookup when `WITH diff` isn't specified for Rangefeeds, so the small (unmeasured) perf hit is strictly opt-in.

Co-authored-by: Nathan VanBenschoten <nvanbenschoten@gmail.com>