Create a new function and action that handles the HTTP request sent from the perflab_start_background_job.

Acceptance Criteria

• Create a custom function and register to the action wp_ajax_background_process_handle_request
  • The function accepts no parameters and takes data from the request
• The function will process the request as follows
  • Verify the request by checking the nonce passed with check_ajax_referer function
    • If the verification fails, the action will return early
  • Verify the job is not currently running
    • Take the $job_id from the HTTP request data
    • Using the job ID, check the job_lock term meta for this specific job
    • If the job_lock term meta is set, the job is running and the action will return early
  • If both checks above past, the job is run by calling the perflab_background_process_run function
    • The perflab_background_process_run is called passing the $job_id as it's only parameter
    • The perflab_background_process_run does not return anything (void)