KAFKA-13533: Clean up resources on failed connector and task startup

[C0urante]

Jira

Introduces and leverages a new Closeables utility class that can be used to track accrued AutoCloseable objects via a try-with-resources block. Also switches the Worker class over to use Plugins::withClassLoader wherever possible.

Committer Checklist (excluded from commit message)

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

[C0urante]

@tombentley FYI, I've finished rebasing this.

[C0urante]

Downgrading to a draft until I can revisit and fix the merge conflicts.