The Session should not be injected as a service anymore. Rather, the
request stack should be used to get the session from the current http
request.

In addition some unused session services have been removed from DI

Todo:
[] - Use the symfony driver (browserkit) as default driver to run the
tests on. Now we seem to use Selenium2 with Chrome by default. And that
causes some of the tests to fail. Wayf tetss for example are unable to
click certain links because they are not on the page?
[] - Sessions are not stable yet. The authentication state is lost
regularly. Seems to relate to the loop guard section that is commented
out in: src/OpenConext/EngineBlockBundle/EventListener/AuthenticationStateInitializer.php
[] - I started running the different features, and fixed some issues
here and there. But I suggest to use the failing tests to find/fix the
remaining issues present in the EB upgrade

- Install a new Pimple version to keep DiContainer in the air
- Enabled Symfony flex to ensure we only install SF 5.4 packages
- APCU was disabled as the cache adapter for doctrine
- app.php was butchered, needs further optimization and fixing
- SamlValueObject was upgraded to a version supporting PHP8 (dev)