Bug 32354: Accept session_state param given by OAuth IdP

Bug 32354: Accept session_state param given by OAuth IdP

This patch ensures Koha doesn't throw an error if the IdP hands back a
session_state parameter.

To test:

1) Set up an identity provider
2) On the IdP's configuration, make it hand back a session_state
3) Confirm authentication using OIDC works with and without the
session_state

Sponsored-by: Plant & Food Research
Signed-off-by: David Cook <dcook@prosentient.com.au>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>