[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.Rest/Entities/Interactions/InteractionHelper.cs

@@ -522,6 +522,17 @@ namespace Discord.Rest
 
             return client.ApiClient.CreateInteractionResponseAsync(apiArgs, interactionId, interactionToken, options);
         }
+
+        public static async Task RespondWithPremiumRequiredAsync(BaseDiscordClient client, ulong interactionId,
+            string interactionToken, RequestOptions options = null)
+        {
+            await client.ApiClient.CreateInteractionResponseAsync(new InteractionResponse
+            {
+                Type = InteractionResponseType.PremiumRequired,
+                Data = Optional<InteractionCallbackData>.Unspecified
+            }, interactionId, interactionToken, options);
+        }
+
         #endregion
 
         #region Guild permissions