Add SESSION_STORE options (#5403)

* Allow configuring the session storage driver

Fixes #3814

* Document SESSION_STORE env var

* Add missing dependency

* Docs tweak

api/src/controllers/auth.ts

@@ -1,5 +1,4 @@
 import { Router } from 'express';
-import session from 'express-session';
 import grant from 'grant';
 import Joi from 'joi';
 import ms from 'ms';
@@ -219,8 +218,6 @@ router.get(
 	respond
 );
 
-router.use('/oauth', session({ secret: env.SECRET as string, saveUninitialized: false, resave: false }));
-
 router.get(
 	'/oauth/:provider',
 	asyncHandler(async (req, res, next) => {