Add some HTTP error codes to POST endpoint

[jordan2175]

We should probably add some more common HTTP error codes POST endpoints.

[varnerac]

• 403: Attempt to write to a collection where can_write returns `false
• 404: API Root and/or Collection aren't available
• 413: POSTed Payload exceeds max_content_length of API Root
• 415: Attempt to POST objects with a content type the server does not support

[jordan2175]

The errors code for a POST are now defined as:

202 - The request was successful accepted

401 - The client needs to authenticate.

403 - The client does not have access to write to this resource.

404 - The client can not write to this resource or it is not available.

413 - The POSTed payload exceeds the max_content_length of the API Root.

415 - The client attempted to POST a payload with a content type the server does not support.

422 - The object type or version is not supported or could not be processed. This can happen, for example, when sending a version of STIX that this TAXII Server does not support and cannot process, when sending a malformed body, or other unprocessable content.