docs(debugging): update post body json to remove capital `Job`

[michaelpeterswa]

I noticed it says in CONTRIBUTING.md that this project isn't accepting contributions, but hopefully a small documentation change is allowed. The capital J in job creates the following error in the frontend service (/v1alpha1/createJob endpoint) which is a bit unclear if you don't notice the extra capital:

{
    "code": 6,
    "message": "Duplicate job_request_id provided: job_request_id= is not unique.",
    "details": [
        {
            "reason": "DUPLICATE_JOB_KEY",
            "domain": "",
            "metadata": {
            }
        }
    ]
}

This PR addresses that small inconsistency to match the example provided here GCP Aggregation Service - Testing The System

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[rulohani]

Thanks for the doc update, Michael. We will update it in the repo.

[hostirosti]

This has been addressed, thank you for your contribution @michaelpeterswa.