Return HTTP 200 status code from HTTP PUT requests for OSCAL root objects

[pkothare]

We should consider returning the result return from oscalObjectService.save here since the business logic may change the object during that call.

For example, we currently set last modified, but in the future I could envision actions like hashes being computed and stored or validation being recorded.

The REST definition responses do not reflect this (for this and other request methods) and should be updated, either as part of this parent story or a separate issue.

Originally posted by @rgauss in EasyDynamics/oscal-rest-service#56 (comment)