Add Turnstile link to Managed Challenges doc (#17859)

Author: patriciasantaana

src/content/docs/waf/reference/cloudflare-challenges.mdx

@@ -50,6 +50,7 @@ Currently, **Managed Challenge** actions are available in the following security
 - [User Agent Blocking](/waf/tools/user-agent-blocking/)
 - [Firewall rules](/firewall/) (deprecated)
 - [Rate Limiting (previous version, deprecated)](/waf/reference/legacy/old-rate-limiting/)
+- [Turnstile](/turnstile/concepts/widget/#managed-recommended)
 
 ### JS challenge