KAFKA-14500; [4/N] Add Timer interface

[jeffkbkim]

Adds the Timer interface that will be used by the new group coordinator.

• Timer: used by GroupMetadataManager (introduced in KAFKA-14462; [12/N] Add GroupMetadataManager and ConsumerGroup #13639)

Committer Checklist (excluded from commit message)

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

[kirktrue]

Thanks @jeffkbkim!

Any chance you could add @see annotations to the class-level Javadoc that points to where this is used? I see the GitHub PR description states that it's used by the GroupMetadataManager. It's helpful (to me, at least) to see where interfaces like this fit into the bigger picture.

Thanks!

[dajac]

@jeffkbkim Could you update the interface as we discussed offline?

[jeffkbkim]

@kirktrue thanks for the comment. I will do so when GroupMetadataManager is merged to trunk.

@dajac updated the interface.

[dajac]

I left a few minor comments. Should we update the title of the PR as well?

[dajac]

nit: We don't need this because it is an internal interface anyway.

[dajac]

As a second though, I also wonder if we should use a delay instead of a deadline. This may be easier to use. We could also use TimeUnit.

[dajac]

LGTM