Add page iterator

[jasonjoh]

https://docs.microsoft.com/en-us/graph/sdks/paging

[baywet]

To provide some more context here, it would look something like that for consumers:

client := msgraphsdk.NewGraphServiceClient(adapter)
page1, err := client.Users().Get(&opts)
if err != nil {
    log.Fatal(err)
}
users := make([]graph.User, 0)

iterator := msgraphsdk.NewPageIterator(page1, func (item interface{}) (bool, err) {
    users = append(users, item.(graph.User)) //or anything else you want to do with the item
    return false, nil // boolean is used to tell the iterator to stop before the end of the collection
});
ierator.Iterate(); // this would execute the requests as long as next links are returned, and call the callback for each item in the result