New Example: Preserve Query Strings on redirect

[brittandeyoung]

Issue #, if available:

Closes #11
Description of changes:

This PR includes an example and tests for preserving query strings and url when performing a redirect.

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[Knufle]

It would be great to have this merged, thanks!

[kurtextrem]

For anyone finding this, with the runtime v2, it looks like you can just use the querystring prop as string: https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/functions-javascript-runtime-20.html#:~:text=JavaScript%20runtime%202.0.-,Query%20string,-Note (see the Note)

[capelio-gloo]

@kurtextrem While it would have been great for AWS to provide a querystring.stringify function for preserving the original query string when responding with a redirect, unfortunately the one they've made available only works on simple objects, e.g.

{
  "foo": "bar"
}

If you look at the docs (or just console.log an object in the Cloudfront Function web console) the shape of the querystring object on the request event is:

{
  "foo": {
    "value: "bar"
  }
}

Which does NOT work with the querystring.stringify AWS makes available in their Cloudfront JS 2.0 runtime. You're stuck still having to write your own function.