Add additional details aboutworkload-params

[Naarcha-AWS]

Please provide details on how and where the documentation can be improved

Recently, a developer encountered the following issue running Vectorsearch with Mensor:

 File "/home/ec2-user/.pyenv/versions/3.8.0/lib/python3.8/site-packages/osbenchmark/test_execution_orchestrator.py", line 378, in run
    pipeline(cfg)
  File "/home/ec2-user/.pyenv/versions/3.8.0/lib/python3.8/site-packages/osbenchmark/test_execution_orchestrator.py", line 69, in __call__
    self.target(cfg)
  File "/home/ec2-user/.pyenv/versions/3.8.0/lib/python3.8/site-packages/osbenchmark/test_execution_orchestrator.py", line 314, in benchmark_only
    return execute_test(cfg, external=True)
  File "/home/ec2-user/.pyenv/versions/3.8.0/lib/python3.8/site-packages/osbenchmark/test_execution_orchestrator.py", line 273, in execute_test
    raise exceptions.BenchmarkError(result.message, result.cause)
osbenchmark.exceptions.BenchmarkError: Error in test execution orchestrator (Unused workload parameters ['target_index_primary_shards', 'target_index_replica_shards'].) 

On the VectorSearch readme, certain parameters that existed in the error were not present in readme. This is because certain workload-params behaviors do not exist in the documentation.

We should modify the documentation to detail how workload-params can be used. Govnid gave the following summary:

• As the path to a JSON file containing the parameters to pass in, such as /tmp/params.json
• As verbatim JSON, such as { "field": 10 }
• As a list of key-value pairs: a:1,cluster_health:green

Provide references

No response

Additional context

No response

[IanHoang]

Thanks Nate, will insert this into the triage board.