[Spike] New docs: find the best documentation site generator for our needs

[tkajtoch]

Summary

We need a documentation site generator to meet our requirements and help us deliver better documentation quicker.

Acceptance Criteria

• This spike should result in publishing a decision record and getting stakeholders' approvals on the chosen software

Decision drivers

• Supports Markdown, MDX, or similar
• Allows separation of text content and component previews
• Is written in React for easy customization and maintainability
• Supports custom themes
• Is proven to be stable
• Doesn't seem to be at risk of deprecation within the next 3+ years
• Generates static HTML, CSS, and JS without the need to run a dedicated app server
• Supports Markdown/MDX extensions
• Supports or could support full-text search
• Is accessible out-of-the-box and allows for more a11y improvements
• Is SEO-friendly