MINOR: Re-introduce Transformation import to fix TransformationChain Javadoc

[yashmayya]

• The TransformationChain Javadoc has a reference to the Transformation class
• The import was removed (likely accidentally) in https://github.com/apache/kafka/pull/13184/files#diff-be87d8114b5870f9b881cf8c0e6b110951aa990a7d2ad74c886f3a2adb2350db
• It doesn't break the build since we don't generate public Javadocs for this class, but it does affect things like code navigation in IDEs.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[C0urante]

Thanks Yash! LGTM

[C0urante]

Not sure what's going on with Jenkins but I've verified locally that this builds correctly and fixes the relevant Javadocs linking issue. Merging...

[yashmayya]

Thanks Chris! Yeah, the Jenkins thing is odd - no build has been triggered for this merged commit on trunk either. Do we need to raise an Apache INFRA Jira ticket?

[C0urante]

Wild guess with little backing knowledge: I wonder if the queue is just full. It looks like there's two open PRs right now that don't have finished CI runs; the one that was opened earlier is currently running, and the most-recently-opened one doesn't have anything (yet).

If we can rule that out and this starts significantly affecting us, then yeah, an infra ticket is probably warranted 👍