[DNS] Disambiguate Ent customers vs Ent zone plan (#17972)

Author: RebeccaTamachiro

src/content/docs/dns/foundation-dns/index.mdx

@@ -18,7 +18,7 @@ With Foundation DNS, you get access to increased reliability, security, and insi
 
 ## Availability
 
-Foundation DNS is only available to Enterprise plans.
+Foundation DNS is only available to Enterprise customers.
 
 Advanced nameservers are an opt-in configuration. Refer to [set up advanced nameservers](/dns/foundation-dns/setup/).