Add OpenAPI documentation for keep_unmatched field in ocsf mapper processor

[api-clients-generation-pipeline]

See DataDog/datadog-api-spec#5266 Test branch datadog-api-spec/test/sebastien.lubineau/obs-pipelines-ocsf-keep-unmatched

[chatgpt-codex-connector]

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https://github.com/DataDog/documentation/blob/53b531cf74d61ff36d6ba6168f62f186cf2fd0cd/data/api/v2/full_spec.yaml#L97089
Restore BatchRowsQuery operation in v2 API spec

This change removes the entire BatchRowsQuery endpoint (/api/v2/reference-tables/queries/batch-rows) and its request/response schemas from data/api/v2/full_spec.yaml even though the commit is scoped to adding keep_unmatched for OCSF mapping; as a result, generated docs/SDK metadata will stop exposing a previously documented Reference Tables API operation, creating a breaking regression for users that still call that route. The same removal is propagated to menu and examples files, so this is not just a display issue but a spec-level API surface drop.

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