Content-Type header check in response is not handling charset

[dkundel]

Broken:

exports.handler = async (context, event, callback) => {
  const response = new Twilio.Response();
  response.appendHeader('Content-Type', 'application/json; charset=UTF-8');
  response.setStatusCode(400);
  response.setBody(
    {message: 'I am a JSON message'}
  )
  return callback(null, response);
};

Working:

exports.handler = async (context, event, callback) => {
  const response = new Twilio.Response();
  response.appendHeader('Content-Type', 'application/json');
  response.setStatusCode(400);
  response.setBody(
    {message: 'I am a JSON message'}
  )
  return callback(null, response);
};

Instead we should adjust the check for the Content-Type header to validate that it includes application/json as opposed to being explicitly application-json.

https://github.com/twilio-labs/serverless-toolkit/blob/33ca348aa7886cdf58255900077b156f00461433/packages/runtime-handler/src/dev-runtime/internal/response.ts#L139