Update cookie expiration without updating data

[Momy93]

Prerequisites

• [X] I have written a descriptive issue title
• [X] I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

A touch() method (like in @fastify/session) to extend to cookie expiration date, without changing the session data. This could be done by setting changed=true.

Motivation

It's useful in scenarios where the session is extended evey time the client calls some endpoints.

Example

Whenever we want to extend the session, we would do:

request.session.touch();

[jsumners]

Would you like to send a Pull Request to address this issue? Remember to add unit tests.