Add round end Discord pings, discord webhook API (#19468)

Content.Server/Discord/WebhookPayload.cs

@@ -0,0 +1,29 @@
+using System.Text.Json.Serialization;
+
+namespace Content.Server.Discord;
+
+// https://discord.com/developers/docs/resources/channel#message-object-message-structure
+public struct WebhookPayload
+{
+    /// <summary>
+    ///     The message to send in the webhook. Maximum of 2000 characters.
+    /// </summary>
+    [JsonPropertyName("content")]
+    public string Content { get; set; } = "";
+
+    [JsonPropertyName("username")]
+    public string? Username { get; set; }
+
+    [JsonPropertyName("avatar_url")]
+    public string? AvatarUrl { get; set; } = "";
+
+    [JsonPropertyName("embeds")]
+    public List<WebhookEmbed>? Embeds { get; set; } = null;
+
+    [JsonPropertyName("allowed_mentions")]
+    public WebhookMentions AllowedMentions { get; set; } = new();
+
+    public WebhookPayload()
+    {
+    }
+}