[Feature] Premium subscriptions (#2781)

* what a big commit lel, add app sub enums

* work

* ah yup lol

* `?`

* events 1

* typo

* `list` => `get` | remaining events

* add `RespondWithPremiumRequiredAsync` to interaction module base

src/Discord.Net.Core/DiscordConfig.cs

@@ -237,5 +237,10 @@ namespace Discord
         ///     Returns the max amount of tags applied to an application.
         /// </summary>
         public const int MaxApplicationTagCount = 5;
+
+        /// <summary>
+        ///     Returns the maximum number of entitlements that can be gotten per-batch.
+        /// </summary>
+        public const int MaxEntitlementsPerBatch = 100;
     }
 }