add hook for http requests

There's no good way to count read and write requests (e.g. for the sheets v4 api) - which is rate limited.

If this gem allowed the configuration of a lambda for when a http request is made, then the application using this gem would be free to log/count requests and then mitigate over usage.

As it stands now it's a bit of craps shoot. No way to tell when the client is reaching its quota.