Reorganization and first content refinements content

[kosabogi]

This PR focuses on cleaning up and reorganizing the GenAI search high availability reference architecture.

What was done

• Added a new Vector search optimization section
• Reorganized the content to present use cases first, followed by vector search optimization, and then the architecture section
• Organized considerations sections into a new Important considerations section to be more concise and less wordy with headings
• Added links to related documentation pages
• Moved and reframed a paragraph to improve narrative flow: "Promoting the multi–availability zone..." description to serve as the introduction of the Architecture section
• Applied substitutions and minor language cleanup

Some additional language and style cleanup is still needed, along with more links to relevant documentation and resources.

[github-actions]

Vale Linting Results

Summary: 4 warnings, 1 suggestion found

⚠️ Warnings (4)

File	Line	Rule	Message
deploy-manage/reference-architectures/genai-search-high-availability.md	26	Elastic.DontUse	Don't use 'and/or'.
deploy-manage/reference-architectures/genai-search-high-availability.md	39	Elastic.DontUse	Don't use 'very'.
deploy-manage/reference-architectures/genai-search-high-availability.md	58	Elastic.DontUse	Don't use 'very'.
deploy-manage/reference-architectures/genai-search-high-availability.md	128	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'versus' instead of 'vs'.

💡 Suggestions (1)

File	Line	Rule	Message
deploy-manage/reference-architectures/genai-search-high-availability.md	67	Elastic.Wordiness	Consider using 'also' instead of 'In addition'.

---

The Vale linter checks documentation changes against the Elastic Docs style guide.

To use Vale locally or report issues, refer to Elastic style guide for Vale.

[eedugon]

I like a lot the changes, shared some comments.

One thing to consider in the Important consideratoins structure is if we like more the OTP that was before:

vs the new OTP

IMO we are losing interesting navigation on the right bar with this new approach. Just to double check.

[eedugon]

LGTM!