public Optional<String> determineResponseContentType(ToShapeId operationOrError, String documentContentType) {
        return determineResponseContentType(operationOrError, documentContentType, null);
    }
Returns the expected response Content-Type of the given operation
or error.

<p>See {@link #determineResponseContentType(ToShapeId, String, String)}
for documentation on how the content-type is resolved.

@param operationOrError Operation or error to determine the content-type of.
@param documentContentType Content-Type to use for protocol documents.
@return Returns the optionally resolved content-type of the response.
smithy-model/src/main/java/software/amazon/smithy/model/knowledge/HttpBindingIndex.java