Add WebSocket connection support to sandbox documentation

[whoiskatrin]

Summary

Screenshots (optional)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.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.

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/sandbox/	@whoiskatrin, @ghostwriternr, @cloudflare/pcx-technical-writing, @cloudflare/ai-agents

[github-actions]

Preview URL: https://1625015b.preview.developers.cloudflare.com
Preview Branch URL: https://add-websockets-support-to-sandbox.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/sandbox/guides/websocket-connections/	https://add-websockets-support-to-sandbox.preview.developers.cloudflare.com/sandbox/guides/websocket-connections/
https://developers.cloudflare.com/sandbox/api/ports/	https://add-websockets-support-to-sandbox.preview.developers.cloudflare.com/sandbox/api/ports/
https://developers.cloudflare.com/sandbox/concepts/preview-urls/	https://add-websockets-support-to-sandbox.preview.developers.cloudflare.com/sandbox/concepts/preview-urls/
https://developers.cloudflare.com/sandbox/	https://add-websockets-support-to-sandbox.preview.developers.cloudflare.com/sandbox/