Random sampling get stats

[masseyke]

This adds a new rest action and corresponding transport action for fetching stats about a random sample.

[Copilot]

Pull Request Overview

This PR introduces a new REST action and corresponding transport action for fetching statistics about random sampling data. The implementation enables users to retrieve statistics about sampling operations performed on indices through a new /_sample/stats endpoint.

Key changes:

• Added a new GetSampleStatsAction with REST and transport handlers for retrieving sampling statistics
• Updated the SamplingService.SampleStats class to improve field naming, add test constructors, and enhance human-readable time representations
• Added comprehensive test coverage for the new action classes and serialization

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
server/src/main/java/org/elasticsearch/action/admin/indices/sampling/GetSampleStatsAction.java	Core action definition with request/response classes for sampling statistics
server/src/main/java/org/elasticsearch/action/admin/indices/sampling/RestGetSampleStatsAction.java	REST handler implementing the /{index}/_sample/stats endpoint
server/src/main/java/org/elasticsearch/action/admin/indices/sampling/TransportGetSampleStatsAction.java	Transport layer implementation for sampling statistics retrieval
server/src/main/java/org/elasticsearch/ingest/SamplingService.java	Enhanced SampleStats class with improved field naming and test support
server/src/main/java/org/elasticsearch/action/ActionModule.java	Registration of new action and REST handler
Various test files	Comprehensive test coverage for serialization and functionality

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[elasticsearchmachine]

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

[nielsbauman]

I just quickly scanned the actions and left two small comments. I'll leave the rest of the review up to someone who actually knows something about the sampling work :)