Create a new perflab_background_job_is_completed function. This function is used within the background process to determine if the job being run is complete.

Acceptance Criteria

• Create a new perflab_background_job_is_completed function
• The function accepts the $job_id as it's only parameter
• The function returns a boolean
• This function checks if the job is complete by testing if the job_completed_at meta is set. If it is set the job is considered complete.