MINOR: Add logging to OffsetSyncStore

[gharris1727]

This code path is non-trivial, and has no logging that allows us to inspect it's behavior. DEBUG logging should only print intermittently when offsets are being translated and should have fairly reasonable volume. TRACE logging applies to every message in the offset syncs topic, and will represent a significant log volume both during startup and continuous operation.

Committer Checklist (excluded from commit message)

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

[gharris1727]

Closing this as it was only for temporary debug build.