Is it possible to add a "pre-chat" or "post-chat" page on the chatbot in order to either request more information before the chatbot or ask the user to leave a feedback about the chatbot experience?

Yes, the pre-hook is essentially the hook that allows you to write logic that will execute before an intents (all intents fired) fire so you can think of it as an event before. You can also do it on the same thing on the other end before the request (Global Logic) that is applicable to every request. Anytime a request goes through the chatbot, it will go through the pre-hook node.