Middleware does not properly set cookie

[DanielSiepmann]

The middleware, for whataver reason, sets the cookie with a path to /typo3/.
This is unexpected and should be / for the time beeing, as hard coded within the JS.

Even better would be the proper TYPO3 path, but that would need to be exposed to JS which we won't do right now.
So we first need to get rid of the unexpected path within PHP.