Update spring server overview page

[smyrick]

📝 Description

Add some images and more details, copying information from https://medium.com/expedia-group-tech/creating-a-reactive-graphql-server-with-spring-boot-and-kotlin-54aca7316470

🔗 Related Issues

Revamp of #538

🖼 New look

[ghost]

This change is an improvement on several fronts. I'm proposing an addition to specifically address #537.

There was text in #538 to address the specific problem encountered in #537, which I don't see in any of this. (Possibly my ignorance is showing.) Should there be specific mention of Spring WebMVC and/or Spring Servlet somewhere here, even if it's only pointing out that we're not giving examples of those technologies, and users of those technologies will encounter issues they'll have to resolve for themselves? It's not clear to me whether the proposed changes here would prevent someone else from running into the same issue as #537.

[smyrick]

@EXPErdelfavero Added a back a full sentence about the dropping of Spring Web MVC. We did make some assumptions that anyone who has developed on a Spring server knows that "reactive" means they cannot use servlet. Hopefully the above sentence clarifies that without being such a flag.

We want to save the yellow block NOTE: sections for something of higher priority.

[ghost]

@smyrick Thanks. I'd review and approve the text, but hesitate because I've just demonstrated my lack of qualification to perform a technical review. :) The text looks fine from an editorial standpoint.