feat(opensearch sink): add first-class OpenSearch sink

[pront]

Summary

Add a first-class opensearch sink so OpenSearch users can configure their destination directly. It shares the Elasticsearch sink’s configuration and delivery implementation, with its own reference documentation and examples.

Each sink constructor explicitly selects its distribution. With api_version: auto, the OpenSearch sink selects its compatible bulk API without a version probe; the Elasticsearch sink retains its existing version detection. Explicit API-version overrides remain supported. The shared integration suite continues to build the Elasticsearch implementation directly. Two focused tests exercise type: opensearch over HTTP and authenticated HTTPS, including default API selection and gzip delivery.

References

Closes #11738. Builds on the OpenSearch integration coverage in #24652.

Vector configuration

sources:
  input:
    type: stdin
    decoding:
      codec: json
sinks:
  output:
    type: opensearch
    inputs: [input]
    endpoints: ["http://localhost:19200"]
    bulk:
      index: vector-opensearch-e2e
    compression: gzip
    batch:
      max_events: 5
      timeout_secs: 0.1

How did you test this PR?

Tested against OpenSearch 3.6.0 running locally in Colima. All 82 focused tests passed, including 19 integration tests. Separate end-to-end runs with the Vector binary delivered and retrieved all 40 documents over HTTP and authenticated HTTPS, with gzip, default API selection, certificate verification, and required healthchecks.

The focused suite passed through make test with the OpenSearch integration feature enabled and unrelated workspace packages excluded. Live Amazon OpenSearch Service and Serverless were not tested.

Does this PR include user facing changes?

• Yes. A changelog fragment is included.
• No.

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-19T20:23:46.871797Z	50b0644	New commits
🔒 Security Review	✅ Completed 2026-10-19T20:23:05.532035Z	50b0644	New commits

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[datadoghq-integration]

More details

Distribution-aware detection keeps OpenSearch’s unrelated major version from enabling typed bulk requests. Execution validation was blocked by an HTTP 502 while downloading the pinned Rust toolchain.

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