Add CK param to diffs batch endpoint

What does this MR do and why?

Adds the ck param to the diffs batch endpoint to enable HTTP caching

Screenshots or screen recordings

How to set up and validate locally

Enable diffs_batch_cache_with_max_age feature flag

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

#381607 (closed)