rest: add webhook model (#1435)

Author: trinitrotoluene

src/Discord.Net/Rest/Models/Webhook/Webhook.cs

@@ -0,0 +1,33 @@
+using System.Text.Json.Serialization;
+
+namespace Discord.Models
+{
+    public class Webhook
+    {
+        public const int MinWebhookNameLength = 2;
+        public const int MaxWebhookNameLength = 32;
+
+        public const int MinMessageContentLength = 0;
+        public const int MaxMessageContentLength = 2000;
+
+        public const int MinEmbedLimit = 0;
+        public const int MaxEmbedLimit = 10;
+
+        [JsonPropertyName("id")]
+        public Snowflake Id { get; set; }
+        [JsonPropertyName("type")]
+        public WebhookType Type { get; set; }
+        [JsonPropertyName("guild_id")]
+        public Optional<Snowflake> GuildId { get; set; }
+        [JsonPropertyName("channel_id")]
+        public Snowflake ChannelId { get; set; }
+        [JsonPropertyName("user")]
+        public Optional<User> Creator { get; set; }
+        [JsonPropertyName("name")]
+        public string? Name { get; set; }
+        [JsonPropertyName("avatar")]
+        public string? AvatarId { get; set; }
+        [JsonPropertyName("token")]
+        public Optional<string> Token { get; set; }
+    }
+}

src/Discord.Net/Rest/Models/Webhook/WebhookType.cs

@@ -0,0 +1,8 @@
+namespace Discord.Models
+{
+    public enum WebhookType : byte
+    {
+        Incoming = 1,
+        ChannelFollower = 2
+    }
+}