Adds new append function to URL extension

We've added a new method in our URL extension:

append(queryParameters: [String: String])

This means that you can add query parameters to a URL as a dictionary of key value pairs like so:

let url = URL(string: "https://example.com")!
url.append(queryParameters: ["param1" : "value1, "param2" : "value2"]
//url is now: https://example.com?param1=value1&param2=value2