[Feature] App subscriptions №2 (#2784)

* 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

* sharded client fixes for app premium subs

src/Discord.Net.WebSocket/DiscordShardedClient.cs

@@ -518,6 +518,10 @@ private void RegisterEvents(DiscordSocketClient client, bool isPrimary)
 
  client.WebhooksUpdated += (arg1, arg2) => _webhooksUpdated.InvokeAsync(arg1, arg2);
  client.AuditLogCreated += (arg1, arg2) => _auditLogCreated.InvokeAsync(arg1, arg2);
+
+ client.EntitlementCreated += (arg1) => _entitlementCreated.InvokeAsync(arg1);
+ client.EntitlementUpdated += (arg1, arg2) => _entitlementUpdated.InvokeAsync(arg1, arg2);
+ client.EntitlementDeleted += (arg1) => _entitlementDeleted.InvokeAsync(arg1);
  }
 
  public async Task<SocketApplicationCommand> CreateGlobalApplicationCommandAsync(ApplicationCommandProperties properties, RequestOptions options = null)