Add controller and action name to the fragment caching instrumentation payload

This allows tracking the cache activity and performance separately for each controller action. For instance, it would be possible to calculate the cache hit rate for a specific action on a specific controller.

I'd like to add the virtual path of the template to the payload, but it doesn't appear to be accessible from within the module – and I'd rather not pass it explicitly from Action View. If you have any ideas, it would be much appreciated.