Investigate alternative to connect-mongo

[carmenfan]

Description

We're using mongo as our session store via connect-mongo and whilst it's somewhat functional we've been running into issues lately.

1. it has inadequate self healing capabilities (see Session manager doesn't recover from Topology is closed error #5418)
2. occasionally session is not updated as desired (seems to be more prominent on a replica set and if the request is short lived see comment)

Suggested solution

We should look at alternatives (both mongo as storage libraries and also alternative methods to store our sessions)

https://github.com/mongodb-js/connect-mongodb-session is now a suggested alternative

Goal

• As a 3DR admin I want to ensure my session store is robust and updates are committed (or at least throws you an error if it failed

Tasks

TBC