Add 'json()' response format

[allenheltondev]

When I get a response from a get call or a subscription, I'd like the sdk to parse json for me optionally.

I often store stringified json objects as cache items and when I receive a response, it would be a nice developer experience to have it returned as an object. Thinking something like this:

const getResponse = await cacheClient.get('myCache', 'key');
if(getResponse instanceof CacheGet.Hit) {
  const myObject = getResponse.json();
}

If the value is not a stringified object, I'd expect an error to be thrown if this is called.

[allenheltondev]

You can see an example in Postman's documentation here.