Make ban command properly give a ban message instead of a placeholder (#5087)

Content.Server/Database/ServerBanDef.cs

@@ -52,5 +52,19 @@ namespace Content.Server.Database
             BanningAdmin = banningAdmin;
             Unban = unban;
         }
+
+        public string DisconnectMessage
+        {
+            get {
+                var expires = "This is a permanent ban.";
+                if (this.ExpirationTime is { } expireTime)
+                {
+                    var duration = expireTime - this.BanTime;
+                    var utc = expireTime.ToUniversalTime();
+                    expires = $"This ban is for {duration.TotalMinutes:N0} minutes and will expire at {utc:f} UTC.";
+                }
+                return $"You, or another user of this computer or connection, are banned from playing here.\nThe ban reason is: \"{this.Reason}\"\n{expires}";
+            }
+        }
     }
 }