[Tunnel] Quick Tunnel access policies

[hugo-vicente11]

Summary

• Adds a Quick Tunnels get-started page under /tunnel/.
• Documents public tunnels and email authentication using exact addresses, repeated flags, comma-separated lists, and wildcard domains.
• Moves the legacy TryCloudflare page into the standard Tunnel information architecture.
• Adds redirects and updates existing links to the new page.

This PR should remain a draft until --allowed-mail is available in a released version of cloudflared.

Screenshots

Documentation checklist

• A separate changelog commit with a demo GIF will be created when the feature ships.
• The change adheres to the documentation style guide.
• Files which have changed name or location have been allocated redirects.