Changes to POST /consumers/:groupid/instances/:name/assignments

added the optional property validation_errors to the response with the 404 status

added the optional property validation_errors to the response with the 409 status

added required request body

removed the success response with the status 200

api tag Consumers added

added the non-success response with the status 404

added the non-success response with the status 409

added the success response with the status 204

endpoint added