Revise Descriptions When OSCAL Content Returned to Client

[brian-comply0]

Description

As a developer issuing OSCAL REST API calls to retrieve OSCAL content, I need to understand how to request the OSCAL format I require.

Acceptance Criteria

• For each model, the description for the following endpoints is updated as defined below
  • GET /[model-name]/{Identifier}
  • GET /[model-name]/{Identifier}/snapshot/{Identifier}
  • GET /profile/{Identifier}/resolved-catalog
  • GET /profile/{Identifier}/resolved-snapshot/{Identifier}

Description Content

The current description should be maintained for each of the four endpoints, with the following added to that content:

When processing this request, the implementation _must_ honor the `Accept` HTTP header for JSON, XML, and YAML. When `Accept` is set to:
- `application/json` or `application/oscal+json` return the OSCAL content in JSON format;
- `application/xml` (preferred by RFC 7303) or `text/xml` (deprecated by RFC 7303) or `application/oscal+xml` return the OSCAL content in XML format; or
- `application/yaml` or `text/yaml` return the OSCAL content in YAML format.

When returning the OSCAL content, the implementation _must_ set the `Content-type` header to:
- `application/json` when returning the OSCAL content in JSON format;
- `application/xml` when returning the OSCAL content in XML format; or
- `application/yaml` when return the OSCAL content in YAML format.

[brian-comply0]

@mpemy changes look good!

[brian-comply0]

Full addressed in PR #72. Closing.