fix: configure index replicas for the legacy Zeebe ES/OS exporter

[bkenez]

Which problem does the PR fix?

Closes #6430

What's in this PR?

The unified-config remap (#4554) replaced the legacy
zeebe.broker.exporters.<engine>.args.index.numberOfReplicas with the Camunda exporter's unified key.
Those keys drive independent exporters, so the remap dropped the zeebe-record-* replica configuration
entirely (defaulted to 0 since 8.9).

This re-adds numberOfReplicas to the legacy ES/OS exporter, controlled by a new
orchestration.exporters.zeebe.replicas that defaults to orchestration.index.replicas (preserving 8.8
behavior); an explicit value, including 0, is honored. Applied to 8.9 and 8.10. The 8.10 deprecation of
this key (removal in 8.11) is handled in #6317.

Checklist

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• In-repo documentation are updated (if needed).

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[Copilot]

Pull request overview

This PR restores configurability of the legacy Zeebe ES/OS exporter (zeebe-record-*) index replica count for chart versions 8.9 and 8.10 by re-introducing numberOfReplicas into the legacy exporter configuration, with an explicit override that can still honor 0.

Changes:

• Adds orchestration.exporters.zeebe.replicas (nullable) to control legacy exporter index replicas, defaulting to orchestration.index.replicas when unset.
• Renders zeebe.broker.exporters.{elasticsearch,opensearch}.args.index.numberOfReplicas in the unified application config for legacy exporters.
• Updates schema/README and adds unit tests validating inheritance + explicit overrides (including 0), for both ES and OpenSearch paths.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
charts/camunda-platform-8.9/values.yaml	Introduces the new nullable value orchestration.exporters.zeebe.replicas.
charts/camunda-platform-8.9/values.schema.json	Adds schema support for the new value.
charts/camunda-platform-8.9/values.schema.extra.json	Extends the extra schema overlay to include the new value.
charts/camunda-platform-8.9/templates/orchestration/files/_application.yaml	Re-adds numberOfReplicas under legacy ES/OS exporter index config with “inherit unless explicitly set” semantics.
charts/camunda-platform-8.9/test/unit/orchestration/configmap_unified_test.go	Adds unit tests for default inheritance, override, and explicit 0, for ES and OS exporters.
charts/camunda-platform-8.9/README.md	Regenerates docs table to include the new value.
charts/camunda-platform-8.10/values.yaml	Introduces the new nullable value orchestration.exporters.zeebe.replicas.
charts/camunda-platform-8.10/values.schema.json	Adds schema support for the new value.
charts/camunda-platform-8.10/values.schema.extra.json	Extends the extra schema overlay to include the new value.
charts/camunda-platform-8.10/templates/orchestration/files/_application.yaml	Re-adds numberOfReplicas under legacy ES/OS exporter index config with “inherit unless explicitly set” semantics.
charts/camunda-platform-8.10/test/unit/orchestration/configmap_unified_test.go	Adds unit tests for default inheritance, override, and explicit 0, for ES and OS exporters.
charts/camunda-platform-8.10/README.md	Regenerates docs table to include the new value.