Enabled filtering of metrics in the LoggingEmitter

[nozjkoitop]

Fixes #19021.

Description

Added metric filtering support for LoggingEmitter with a default allowlist and optional override path.

Configuration

• Introduced druid.emitter.logging.filterMetrics (default false) to gate metric filtering
• Added druid.emitter.logging.metricAllowlistPath to optionally load a custom allowlist file

Default allowlist now lives in defaultLoggingMetricNames.json and is used when no custom path is provided. Format is simplified to a JSON array of metric names. If a custom allowlist path is configured but missing, emitter falls back to the default built-in allowlist.

Release note

LoggingEmitter can now optionally filter metric logs by an allowlist, which helps reduce log volume on busy clusters while keeping non-metric events unchanged. Enable filtering with druid.emitter.logging.filterMetrics=true, and optionally point druid.emitter.logging.metricAllowlistPath to a JSON with metrics to include, if the custom file is missing, Druid automatically falls back to the built-in default allowlist.

This PR has:

• been self-reviewed.
• 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.

[abhishekrb19]

Thanks @nozjkoitop for the contribution! Cross-linking the comment here on a similar implementation - #19030 (review)