Add settings for health indicator shard_capacity thresholds

[samxbr]

Add dynamic settings to allow user to configure the unhealthy thresholds (yellow/red) of shard capacity health indicator. They replace the current hard-coded values:

• health.shard_capacity.unhealthy_threshold.yellow (default 10)
• health.shard_capacity.unhealthy_threshold.red (default 5)

Behavior:

• both thresholds need to be positive integers
• RED threshold needs to be smaller than YELLOW threshold, so the health indicator follows the order from GREEN -> YELLOW -> RED

Closes #116697

[github-actions]

🔍 Preview links for changed docs

• docs/reference/elasticsearch/configuration-reference/health-diagnostic-settings.md

[github-actions]

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[Copilot]

Pull Request Overview

This PR introduces configurable thresholds for the shard capacity health indicator, allowing administrators to customize when the indicator reports YELLOW and RED statuses. Previously, these thresholds were hardcoded to 10 and 5 remaining shards respectively.

• Adds two new dynamic cluster settings for configuring YELLOW and RED thresholds
• Updates the ShardsCapacityHealthIndicatorService to use configurable thresholds instead of hardcoded values
• Includes comprehensive test coverage and documentation for the new settings

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ShardsCapacityHealthIndicatorService.java	Adds configurable threshold settings with validation and dynamic updates
ShardsCapacityHealthIndicatorServiceTests.java	Updates all tests to use the new constructor and adds threshold validation tests
NodeConstruction.java	Updates service instantiation to pass settings parameter
ClusterSettings.java	Registers the new settings with cluster configuration
HealthFeatures.java	New feature specification for the settings
module-info.java	Exports the new HealthFeatures class
META-INF/services/org.elasticsearch.features.FeatureSpecification	Registers the HealthFeatures service
health-diagnostic-settings.md	Documents the new configuration settings
30_feature.yml	Adds integration tests for the new settings functionality

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[elasticsearchmachine]

Hi @samxbr, I've created a changelog YAML for you.

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[seanzatzdev]

LGTM!

[nielsbauman]

I left one more small cleanup comment, but other than that LGTM.
Thanks a lot for working and iterating on this!

[nielsbauman]

We don't need this healthMetadata anymore.