zapier convert: Add support for auth mapping templating

[eliangcs]

Fixes PDE-64.

Try zapier convert a WB app with the following auth mapping:

zapier convert currently generates the following auth middleware in index.js:

const maybeIncludeAuth = (request, z, bundle) => {
  request.headers['Authorization'] = bundle.authData['AccessKey'];

  return request;
};

which doesn't reflect the actual mapping in the WB app. This PR fixes the issue so that it generates the correct code:

const maybeIncludeAuth = (request, z, bundle) => {
  request.headers['Authorization'] = `AccessKey ${bundle.authData['AccessKey']}`;

  return request;
};

[xavdid]

awesome! i'm so excited about how far this has come.