Fix mark segment unused when overshadowed by zero replica segment

[kfaraz]

Bug

In the MarkOvershadowedSegmentsAsUnused duty, the coordinator marks a segment as unused
if it is overshadowed by a segment currently being served by a historical or broker.
But it is possible to have segments that are eligible for a load rule but require zero replicas to be loaded.
(Such segments can be queried only using the MSQ engine).
If such a zero-replica segment overshadows any other segment, the overshadowed segment will never be
marked as unused and will continue to exist in the metadata store as a dangling segment.

Changes

• In a coordinator run, keep track of segments that are eligible for a load rule but require zero replicas
• Allow the zero-replicas segments to overshadow old segments and hence mark the latter as unused
• Add simulation test to verify new behaviour. This test fails with the current code.
• Clean up javadocs

Release note

Fix bug in the MarkOvershadowedSegmentsAsUnused coordinator duty to also consider segments that are overshadowed by a segment that requires zero replicas.

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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.
• a release note entry in the PR description.
• 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.

[AmatyaAvadhanula]

the coordinator marks a segment as unused if it is overshadowed by a segment currently being served by a historical or broker.

Could you please share when should a segment only on the brokers, but not on any of the historicals, overshadow segments?

[kfaraz]

Could you please share when should a segment only on the brokers, but not on any of the historicals, overshadow segments?

This could be possible for a broadcast segment that is missing from the historicals because of some intermittent issue. The logic regarding the brokers is pre-existing and is not being modified in this PR.

Just to clarify, the segments being considered here are already overshadowed. We are not changing their overshadowed status in any way.
The code in MarkOvershadowedSegmentsAsUnused just decides which overshadowed segments can be marked as unused.

[AmatyaAvadhanula]

Thank you @kfaraz! LGTM

[kfaraz]

Thanks a lot for the prompt review, @AmatyaAvadhanula , @adarshsanjeev !

[cryptoe]

Suggested change

	"Skipping MarkAsUnused until [%s] have elapsed after coordinator start time[%s].",
	"Skipping MarkAsUnused until [%s] have elapsed after coordinator start time [%s] ms.",

[kfaraz]

Sorry, @cryptoe , I saw your comment after the PR was merged. I will try to include this refactor in a later PR.