Migrate IndexToolsAdapter to OS Java client

[moesterheld]

Description

Migrates IndexToolsAdapter to OS Java client

/nocl internal change

Motivation and Context

closes #25016

How Has This Been Tested?

added new IT

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have requested a documentation update.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[Copilot]

Pull request overview

This PR migrates the IndexToolsAdapter for OpenSearch 3 from the deprecated Rest high-level client to the official OpenSearch Java client. The migration maintains full backward compatibility while modernizing the underlying client implementation.

Changes:

• Replaced IndexToolsAdapterOS2 with IndexToolsAdapterOS using the official OpenSearch Java client
• Added comprehensive integration tests for IndexToolsAdapter across all storage backends
• Updated module bindings and test infrastructure to use the new implementation

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
graylog2-server/src/test/java/org/graylog2/indexer/IndexToolsAdapterIT.java	New abstract integration test base class with comprehensive test coverage for count and fieldHistogram methods
graylog-storage-opensearch3/src/test/java/org/graylog/storage/opensearch3/testing/AdaptersOS.java	Updated test adapter factory to instantiate IndexToolsAdapterOS with OfficialOpensearchClient
graylog-storage-opensearch3/src/test/java/org/graylog/storage/opensearch3/IndexToolsAdapterOSIT.java	New OpenSearch3-specific integration test implementation extending base test class
graylog-storage-opensearch3/src/main/java/org/graylog/storage/opensearch3/OpenSearch3Module.java	Updated dependency injection binding to use IndexToolsAdapterOS instead of IndexToolsAdapterOS2
graylog-storage-opensearch3/src/main/java/org/graylog/storage/opensearch3/IndexToolsAdapterOS2.java	Removed deprecated implementation using Rest high-level client
graylog-storage-opensearch3/src/main/java/org/graylog/storage/opensearch3/IndexToolsAdapterOS.java	New implementation using official OpenSearch Java client with equivalent functionality
graylog-storage-opensearch2/src/test/java/org/graylog/storage/opensearch2/IndexToolsAdapterOS2IT.java	Added integration tests for OpenSearch2 adapter for consistency

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[todvora]

LGTM, thanks!