feat(exapp_development): add Kubernetes setup instructions

[edward-ly]

Summary

• Moved the FAQ page on scaling to its own 'Scaling ExApps' section, with new content placed in sub-sections. Text is also updated accordingly.
• The new content was originally written by @oleksandr-nc in Markdown. I converted the text to .rst format via pandoc and cleaned up some of the text and formatting.
• Cosmetic changes such as converting text diagrams to Mermaid may be done at a later time.

🖼️ Screenshots

• TODO