Add more non-platform extensions to dev services guide + make guide guide-ier

[holly-cummins]

It's been a pain point for me for a while that the dev services guide, https://quarkus.io/guides/dev-services, is more of a reference which lists available dev services. The title calls it "Dev Services Overview" and we link to it in that context, but it's would be hard to learn much about dev services, just from that document. I've added a bit more information, and also a few more headings, just to visually bulk up the "this document tells you what a dev service is and how you might use it" section of the document.

The other thing this change does is resolves quarkusio/quarkusio.github.io#1869, which was created in response to quarkiverse/quarkus-wiremock#70. At the moment the decision about what dev services to include is a bit arbitrary - it's mostly platform-only, but Neo4J is in there.

Longer term, hand-curating a list of every ecosystem extension isn't very scalable, so we'll want to investigate automation, and also a solution to the "how can I find out what extensions have dev services?" question. I've raised quarkusio/extensions#983 to partially cover that requirement.

[gsmet]

I think Neo4j was in there because it was part of the core repository at some point.

[holly-cummins]

I think Neo4j was in there because it was part of the core repository at some point.

Yeah, I came to the same conclusion.

[oleg-nenashev]

Thanks, it is definitely a good improvement 🚀

[quarkus-bot]

Status for workflow Quarkus Documentation CI

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It should be safe to merge provided you have a look at the other checks in the summary.

[gsmet]

Nice, thanks!

[github-actions]

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