Improve Performance and Optimizations pages

[Blargian]

Summary

• Gives logical order to the sidebar (following from top to bottom: foundational concepts -> best practices -> tools and analysis -> testing and deployment)
• removes broken page
• reorders index page to match sidebar

Checklist

• Delete items not relevant to your PR
• URL changes should add a redirect to the old URL via https://github.com/ClickHouse/clickhouse-docs/blob/main/docusaurus.config.js
• If adding a new integration page, also add an entry to the integrations list here: https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/en/integrations/index.mdx