Add AS::Notifications to YouTube requests

Opening this PR for discussion.

ActiveSupport::Notifications, by convention, should be namespaced right-to-left, so I've named this `request.yt` (feel free to change this though).

Could be useful for:
  * Quota / Request analysis
  * Time spent making YouTube requests
  * Audit Trails
Let me look into this more - I'm pretty sure you want to treat the payload the same way you'd treat payload to a background job: should be simple values, not complex objects.

I think ActiveSupport::Notifications is built to use custom queuing libraries and I want to make sure this won't conflict.