feat: add exclude sources clone query mode

[jtuglu1]

Description

This adds a case to the cloneQueryMode query context which only mirrors queries to cloned servers. While this can result in partial query results, this allows for things like mirroring traffic/load testing on cloned servers.

Release note

Add excludeSources option to cloneQueryMode query context parameter.

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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.

[FrankChen021]

Severity	Findings
P0	0
P1	1
P2	0
P3	0
Total	1

excludeSource queries can return cached data for segments that are not served by clone targets when broker segment cache has entries from prior normal queries.

Reviewed 9 of 9 changed files.

Findings that could not be attached inline:

• server/src/main/java/org/apache/druid/client/CachingClusteredClient.java:364 - [P1] excludeSource can reuse source-backed cache entries. With broker segment cache enabled, pruneSegmentsWithCachedResults runs before groupSegmentsByServer applies ServerSelector.pick(..., EXCLUDESOURCE). A prior non-excludeSource query can populate the same segment cache key for a segment that is not on any clone; the excludeSource query then removes that segment from remote querying and merges the cached rows, even though the new mode says segments missing from clones should be omitted. This defeats clone-only load tests and can turn expected partial results into full/source-backed results. Disable broker cache for EXCLUDESOURCE or make cache lookup/keying depend on clone availability/mode.

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This is an automated review by Codex GPT-5.5