Add note about Kubernetes Kit not being compatible with Spring Session

[TatuLund]

See: vaadin/flow#17799

[github-actions]

AI Language Review

In the updated documentation file, getting-started.asciidoc, a note regarding compatibility with the Kubernetes Kit is introduced. Specifically, it advises not to include the Spring Session dependency with Hazelcast, as it is incompatible with the Kubernetes Kit. This addition is clear and accurate, enhancing the documentation by providing essential compatibility information. No further improvements are required for this modification.

[mcollovati]

Just adding the hazelcast example could give the false impression that the issues with Spring Session are only related to Hazelcast.
I would suggest adding a Limitations paragraph (or an admonition) right after Requirements, explicitly stating that Spring Session is not supported by Kubernetes Kit.

[heruan]

It's not really about Kubernetes Kit, we got feedback from people trying to use Spring Session with Flow only (free tier). Then after some struggling they reach out to us and learn about Kubernetes Kit, as an alternative to Spring Session.

Probably the note about incompatibility should be (also) in Flow's documentation.

[TatuLund]

@mcollovati & @heruan , should the right place be around these hoods: https://vaadin.com/docs/latest/flow/integrations/spring , e.g. adding there mentioning that for session serialization one needs to use Kubernetes Kit instead of Spring Session?

[mcollovati]

@TatuLund https://vaadin.com/docs/latest/flow/integrations/spring seems a good place to put a note.
But instead of saying that one needs to use Kubernetes Kit instead of Spring Session, I would say something like that currently Vaadin does not support Spring Session out-of-the-box but Kubernetes Kit can be used as an alternative, stating that it is a commercial component.

I wonder if we should link or provide a brief summary of the following comments to explain the reasons:

vaadin/kubernetes-kit#4 (comment)
vaadin/kubernetes-kit#10