Add support for adding data to a new session within the same request-response cycle as destroying a session

[jbr]

No description provided.

[Fishrock123]

Maybe a reset would be better?

[nevercast]

Could also be achieved with a destroy_immediately() followed by a regenerate() - I would specifically like to ensure that the backend store removes the current id, and that I use a new one going forward. There is no clean way to do this currently.