Cleanup expired Sessions / Document Session Cleanup Possibilities

[pujux]

Is your feature request related to a problem? Please describe.

As described in #1425, there currently is no way of cleaning up the expired sessions Vendure creates which can lead to alot of rows in the database over time that just aren't of any use.

Describe the solution you'd like

It should be clearly documented, that there is no periodic cleanup of expired sessions by Vendure and at least there should be functionality exposed for users to call a method that cleans up all expired sessions.

Furthermore, documentation on how to setup a custom CLI script that will call this method would be good. Even better, this custom CLI script could be shipped with the @vendure/create tool so that users can easily call this script periodically with their preferred way of scheduling script execution.

Describe alternatives you've considered

Writing a script on my own to run a DB query and execute a delete query against all expired sessions.

[michaelbromley]

The docs could be added to the deployment section under the heading "running scheduled tasks" which includes the general approach as well as the specific example of cleaning up sessions.