Add DM support

Myriad/Rest/DiscordApiClient.cs

@@ -120,6 +120,9 @@ namespace Myriad.Rest
             _client.PostMultipart<Message>($"/webhooks/{webhookId}/{webhookToken}?wait=true",
                 ("ExecuteWebhook", webhookId), request, files)!;
 
+        public Task<Channel> CreateDm(ulong recipientId) =>
+            _client.Post<Channel>($"/users/@me/channels", ("CreateDM", default), new CreateDmRequest(recipientId))!;
+
         private static string EncodeEmoji(Emoji emoji) =>
             WebUtility.UrlEncode(emoji.Name) ?? emoji.Id?.ToString() ??
             throw new ArgumentException("Could not encode emoji");

Myriad/Rest/Types/Requests/CreateDmRequest.cs

@@ -0,0 +1,4 @@
+namespace Myriad.Rest.Types.Requests
+{
+    public record CreateDmRequest(ulong RecipientId);
+}