Shorter TTL for anonymous sessions

We should have a short (1 hour ?) for anonymous sessions, and use the configurable Settings.gitlab['session_expire_delay'] only for authenticated sessions.

This would avoid creating a whole bunch of anonymous sessions, that consume RAM on our redis fleet (That's why this issue is confidential).

As @andrewn mentioned in https://gitlab.com/gitlab-com/infrastructure/issues/4417#note_82375124:

Application changes around different expiry times for anonymous vs. authenticated sessions (@andrewn to create the issue and ping @DouweM and @reprazent on it)