Suggestion: a custom name instead of req.session

Hello! 👋

Thank you for this package!

I'm considering contributing some code.

In a project I'm working on I'd like to utilize two separate sessions with different SameSite settings for the same endpoint.

If I understand correctly, it's not possible at the moment due to `req.session` and `req.sessionOptions` not being customizable.

Would a PR be welcomed?