Docs: Relabel Server Side Search

[benjaoming]

Relabling these articles. We should separate references and explanations and not gather them under domain-specific subtopics.

Aside from that, I kept changes minimal here as the articles went under a recent review.

Open question: Is "Server Side Search" to be understood as a proper noun? Or should we just say "server-side search"?

I removed the local TOCs as we haven been using that in many other places.

Refs: #9746

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📚 Documentation previews 📚

• User's documentation (docs): https://docs--9897.org.readthedocs.build/en/9897/

• Developer's documentation (dev): https://dev--9897.org.readthedocs.build/en/9897/

[benjaoming]

There was also a suggestion to change the title of the explanation article to "Fast server-side search" - I do think it sounds better because it puts emphasis on one of the most important aspects of switching from the built-in search of Sphinx (and MkDocs in the future?).

[ericholscher]

I agree the local TOC's are not great, and we should likely just have them in the theme like many other themes (eg. Furo)