Small content refinements

[kosabogi]

This PR contains small content refinements on the GenAI High Availability page.

[github-actions]

Vale Linting Results

Summary: 3 warnings found

⚠️ Warnings (3)

File	Line	Rule	Message
deploy-manage/reference-architectures.md	35	Elastic.DontUse	Don't use 'and/or'.
deploy-manage/reference-architectures.md	35	Elastic.DontUse	Don't use 'and/or'.
deploy-manage/reference-architectures.md	35	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'and so on' instead of 'etc'.

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[eedugon]

LGTM! thanks!