[Feature] Update webhook implementation (#2723)

* initial commit

* add partial guild & channel props

* Apply suggestions from code review

Co-authored-by: Quin Lynch <49576606+quinchs@users.noreply.github.com>

---------

Co-authored-by: Quin Lynch <49576606+quinchs@users.noreply.github.com>

src/Discord.Net.Core/Entities/Webhooks/IWebhook.cs

@@ -9,7 +9,7 @@ namespace Discord
     public interface IWebhook : IDeletable, ISnowflakeEntity
     {
         /// <summary>
-        ///     Gets the token of this webhook.
+        ///     Gets the token of this webhook; <see langword="null"/> if the <see cref="Type"/> is <see cref="WebhookType.ChannelFollower"/>.
         /// </summary>
         string Token { get; }
 
@@ -17,10 +17,12 @@ namespace Discord
         ///     Gets the default name of this webhook.
         /// </summary>
         string Name { get; }
+
         /// <summary>
         ///     Gets the ID of this webhook's default avatar.
         /// </summary>
         string AvatarId { get; }
+
         /// <summary>
         ///     Gets the URL to this webhook's default avatar.
         /// </summary>
@@ -30,10 +32,11 @@ namespace Discord
         ///     Gets the channel for this webhook.
         /// </summary>
         IIntegrationChannel Channel { get; }
+
         /// <summary>
-        ///     Gets the ID of the channel for this webhook.
+        ///     Gets the ID of the channel for this webhook; <see langword="null"/> for <see cref="WebhookType.Application"/> webhooks.
         /// </summary>
-        ulong ChannelId { get; }
+        ulong? ChannelId { get; }
 
         /// <summary>
         ///     Gets the guild owning this webhook.
@@ -54,6 +57,11 @@ namespace Discord
         /// </summary>
         ulong? ApplicationId { get; }
 
+        /// <summary>
+        ///     Gets the type of this webhook.
+        /// </summary>
+        WebhookType Type { get; }
+
         /// <summary>
         ///     Modifies this webhook.
         /// </summary>

src/Discord.Net.Core/Entities/Webhooks/WebhookType.cs

@@ -1,14 +1,25 @@
-namespace Discord
+namespace Discord;
+
+/// <summary>
+///     Represents the type of a webhook.
+/// </summary>
+/// <remarks>
+///     This type is currently unused, and is only returned in audit log responses.
+/// </remarks>
+public enum WebhookType
 {
     /// <summary>
-    /// Represents the type of a webhook.
+    ///     An incoming webhook.
     /// </summary>
-    /// <remarks>
-    /// This type is currently unused, and is only returned in audit log responses.
-    /// </remarks>
-    public enum WebhookType
-    {
-        /// <summary> An incoming webhook </summary>
-        Incoming = 1
-    }
+    Incoming = 1,
+
+    /// <summary>
+    ///     A channel follower webhook.
+    /// </summary>
+    ChannelFollower = 2,
+
+    /// <summary>
+    ///     An application (interaction) webhook.
+    /// </summary>
+    Application = 3,
 }