fix: Added missing statsd mappings, updated mappings dimensions and metrics docs to reflect the emitted Coordinator stats

[pirvtech]

Description

Metrics published by various Druid services are handled by the configured Emitter to send them to external observability systems. The Statsd Emitter is used to send to StatsD system. This emitter uses a default mapping file (packaged within Druid) to map from Druid metric types to StatsD metric types. If a mapping is not present for a metric, it is not emitted.

A number of metrics are missing mappings or have incomplete or incorrect dimensions specified in the mappings. It is likely because these mappings are not being kept up-to-date, with the additions and changes to published metrics in the code.

This change updates these mappings for Coordinator metrics and fixes documentation where it deviates from what is in the code.

Release note

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Fixes missing Coordinator stats not being published to StatsD system

This PR has:

• [ x] 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	0
P2	3
P3	0
Total	3

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This is an automated review by Codex GPT-5

[FrankChen021]

I reviewed the follow-up changes. All three prior statsd mapping threads appear resolved in the current code: clone-drop keeps the emitted server dimension, cancelled compaction tasks keep dataSource, and broker sync metrics include their emitted configType and server dimensions.

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This is an automated review by Codex GPT-5

[pirvtech]

Any other comments or is it good to merge?