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

Content.Server/Discord/WebhookEmbedFooter.cs

@@ -0,0 +1,17 @@
+using System.Text.Json.Serialization;
+
+namespace Content.Server.Discord;
+
+// https://discord.com/developers/docs/resources/channel#embed-object-embed-footer-structure
+public struct WebhookEmbedFooter
+{
+    [JsonPropertyName("text")]
+    public string Text { get; set; } = "";
+
+    [JsonPropertyName("icon_url")]
+    public string? IconUrl { get; set; }
+
+    public WebhookEmbedFooter()
+    {
+    }
+}