Create conflict error + mapper

The profile-API, openvsx-API, and uss-API all have at least one instance of an endpoint returning a 409 CONLICT response. The javax.ws.rs package does not contain a matching error so we will have to create a custom one. This error should have the ability to set headers since the USS-API returns an Etag header when the incoming If-Match header is invalid or missing on a create/update operation.