Which was occuring in chrome, where background requests to the PWA
manifest, or opensearch, endpoint caused OIDC to fail due to lost state
since it was only flashed to the session.
This persists it with a manual TTL.
Added tests to cover.
Manually tested against Azure.
For #5929
Extracted logout to the login service so the logic can be shared instead
of re-implemented at each stage. For this, the SocialAuthService was
split so the driver management is in its own class, so it can be used
elsewhere without use (or circular dependencies) of the
SocialAuthService.
During review of #4467
