[frontend-api] avoid session starting in FE API

[vitek-rostislav]

Q	A
Description, reason for the PR	FE API is stateless hence it does not use the session. The problem is the session is started for each GraphQL query anyway. In our code, the session is started even in the FE API for two reasons: 1) autowiring of FlashBagInterface Symfony service anywhere in the application -> the session is started during the build of the container (see symfony/symfony#36063); 2) CartMigrationFacade is defined as an event listener that listens on the kernel.controller event, therefore it is triggered even in the API requests. The facade was originally used in the Twig frontend only so it uses the session, but in the API requests, it does not work (and does not make any sense there). Besides the fact the session is useless in the API, it can be also dangerous as Redis can get overwhelmed by the huge number of pointless session entries.
New feature	No
BC breaks	Yes
Fixes issues	...
Have you read and signed our License Agreement for contributions?	Yes

[sonarcloud]

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0.0% Duplication

[vitek-rostislav]

Hi @pk16011990, on a project, we encountered a very weird behavior - there was added a session entry in the Redis after doing a request on the storefront. The checker did not reveal this error because, at the time of its execution, the session was not started yet. This makes me think we should ensure the checker is called later than it is called now.

On the project, there was LogoutExceptionSubscriber service set as lazy. The subscriber was not called but I think that thanks to the lazy loading it was probably initialized after SessionChecker::onKernelResponse() was called so we could not be aware of the problem with the started session.

In this PR, the problem is resolved thanks to the usage of FlashBagProvider in LogoutExceptionSubscriber but I believe we should investigate the behavior described above and make the checker more reliable even in such edge-case scenarios.