DGS-18914 Add latest caches at the SR client level

[rayokota]

Currently there are caches for latest versions at the serdes level, but those cache more than the plain HTTP responses. This PR adds caches at the SR client level as well.

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
_{Please push an empty commit if you would like to re-run the checks to verify CLA status for all contributors.}