Support caching depending on response content

[ratzrattillo]

It would be great, if we could decide depending on the response content (response body, not only headers), if a response should be cached or not. This might be implemented using event hooks as suggested in https://github.com/karpetrosyan/hishel/pull/204/commits/0b742456e9a4410754adfe5e5605922ae0edd490.