Create forum posts with DiscordWebhookClient (#2603)

src/Discord.Net.Rest/API/Rest/CreateWebhookMessageParams.cs

@@ -42,6 +42,9 @@ namespace Discord.API.Rest
         [JsonProperty("file")]
         public Optional<MultipartFile> File { get; set; }
 
+        [JsonProperty("thread_name")]
+        public Optional<string> ThreadName { get; set; }
+
         public IReadOnlyDictionary<string, object> ToDictionary()
         {
             var d = new Dictionary<string, object>();
@@ -70,6 +73,8 @@ namespace Discord.API.Rest
                 payload["allowed_mentions"] = AllowedMentions.Value;
             if (Components.IsSpecified)
                 payload["components"] = Components.Value;
+            if (ThreadName.IsSpecified)
+                payload["thread_name"] = ThreadName.Value;
 
             var json = new StringBuilder();
             using (var text = new StringWriter(json))

src/Discord.Net.Rest/API/Rest/UploadWebhookFileParams.cs

@@ -22,6 +22,7 @@ namespace Discord.API.Rest
         public Optional<AllowedMentions> AllowedMentions { get; set; }
         public Optional<ActionRowComponent[]> MessageComponents { get; set; }
         public Optional<MessageFlags> Flags { get; set; }
+        public Optional<string> ThreadName { get; set; }
 
         public UploadWebhookFileParams(params FileAttachment[] files)
         {
@@ -51,6 +52,8 @@ namespace Discord.API.Rest
                 payload["allowed_mentions"] = AllowedMentions.Value;
             if (Flags.IsSpecified)
                 payload["flags"] = Flags.Value;
+            if (ThreadName.IsSpecified)
+                payload["thread_name"] = ThreadName.Value;
 
             List<object> attachments = new();