Kept the prototype out of search engines in the Website service.

Services/Website/Sources/Library/Public/Extensions/ConfigKey+Constants.swift

@@ -107,5 +107,7 @@ extension ConfigKey {
     public enum Site {
         /// The configuration key for the public origin the site is served at (scheme and host, no trailing slash).
         public static let origin: ConfigKey = "site.origin"
+        /// The configuration key for letting search engines index the site.
+        public static let indexable: ConfigKey = "site.indexable"
     }
 }