Importer concurrency mode is not fully functional for Opensearch

[sdorokhova]

Describe the bug

The functionality implemented within https://github.com/camunda/operate/issues/6477 is not fully working for variables and events.

To Reproduce

Following tests are failing when run on Opensearch:

VariableZeebeRecordProcessorIT
EventZeebeRecordProcessorIT

This is the case when some of the script parameters contain nulls.

Also described here.

Environment

• Operate Version: 8.5.1, 8.6.0-alpha1

Additional context

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Acceptance Criteria

Definition of Ready - Checklist

• The bug has been reproduced by the assignee in the environment compatible with the provided one; otherwise, the issue is closed with a comment
• The issue has a meaningful title, description, and testable acceptance criteria
• The issue has been labeled with an appropriate Bug-area label
• Necessary screenshots, screen recordings, or files are attached to the bug report

For UI changes required to solve the bug:

• Design input has been collected by the assignee

Implementation

🔍 Root Cause Analysis

💭 Proposed Solution

👉 Handover Dev to QA

• Changed components:
• Side effects on other components:
• Handy resources:
  BPMN/DMN models, plugins, scripts, REST API endpoints + example payload, etc :
• Example projects:

• Commands/Steps needed to test; Versions to validate:

• Docker file / HELM chart : in case that it needed to be tested via docker share the version contain the fixed along with version of other services .

• Release version ( in which version this fixed/feature will be released):

📗 Link to the test case