[Gateway] Add availability note to sandboxing (#17241)

Author: maxvp

src/content/docs/cloudflare-one/policies/gateway/http-policies/file-sandboxing.mdx

@@ -7,6 +7,10 @@ sidebar:
 
 import { Render, Details } from "~/components";
 
+:::note
+Only available on Enterprise plans. For more information, contact your account team.
+:::
+
 In addition to [anti-virus (AV) scanning](/cloudflare-one/policies/gateway/http-policies/antivirus-scanning/), Gateway can quarantine previously unseen files downloaded by your users into a sandbox and scan them for malware.
 
 While the files are quarantined, Gateway will present a scanning page to your users. If a file passes scanning, Gateway will release the file from quarantine and download it to your user's device.