feat: realtime kit docs

[roerohan]

Summary

Adding documentation for realtime kit - moving this from docs.realtime.cloudflare.com to docs.cloudflare.com

Screenshots (optional)

Documentation checklist

• The documentation style guide has been adhered to.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[hyperlint-ai]

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PR Change Summary

Updated the RealtimeKit documentation to include new guides and resources for users.

• Added a new 'Guides' section for RealtimeKit documentation
• Introduced detailed guides on capabilities such as recording, webinars, and webhooks
• Included quickstart resources for live video and voice integration

Added Files

• src/content/docs/realtime/realtimekit/guides/index.mdx
• src/content/docs/realtime/realtimekit/index.mdx
• src/content/docs/realtime/realtimekit/partials/_product-section.mdx

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