Add javadoc and test for Granularity configs in Compaction / Auto Compaction

[maytasm]

Add javadoc and test for Granularity configs in Compaction / Auto Compaction

Description

This is a followup to #10900

• Add javadocs
• Add tests
• Rename variables

Note that there is no functionality change in this PR

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[suneet-s]

Thanks for the fast follow! LGTM

[asdf2014]

👍