GetJobSpecification and GetJobSpecifications are not returning 404 if the job is not found

[arinda-arif]

Describe the bug GetJobSpecification and GetJobSpecifications are not returning 404 if the job is not found.

Expected behavior

• If no job is found, should return 404 instead of 200 with an empty job.
• Any caller can handle it gracefully based on the need
• For external resource managers (being used when resolving job upstreams externally), if receiving a 404 response it will not return an error.