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

Content.Server/Discord/WebhookMentions.cs

@@ -0,0 +1,18 @@
+using System.Text.Json.Serialization;
+
+namespace Content.Server.Discord;
+
+public struct WebhookMentions
+{
+    [JsonPropertyName("parse")]
+    public HashSet<string> Parse { get; set; } = new();
+
+    public WebhookMentions()
+    {
+    }
+
+    public void AllowRoleMentions()
+    {
+        Parse.Add("roles");
+    }
+}