[TASK] Refactor Camunda Helm chart 8.7 to use unified Camunda image

[aabouzaid]

Related to

Epic: https://github.com/camunda/distribution/issues/312

Overview

Starting from Camunda 8.7, we will use the unified Camunda image, which will replace the orchestration components (Zeebe, Operate, Optimize, Tasklist, and later also Identity).

Actions

Sub-tasks

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1. Use the unified Camunda image.
2. Disable old components (Zeebe, Zeebe Gateway, Operate, Optimize, Tasklist, but keep Identity for now).
3. Ensure all components work together as expected, especially with the new Execution Identity.