Switching to unified docker images in 8.9

We will be stopping production of the camunda/operate and camunda/tasklist Docker images starting with version 8.9. Going forward, only the unified camunda/camunda image will be produced.
Tracked in: https://github.com/camunda/camunda/issues/50159
Please confirm that camunda/operate and camunda/tasklist are no longer used in the team so we can proceed with removing the build pipelines.