Add pardon command and tests (#3190)

* Add pardon command

* Make pardoning check for an existing ban and unban first

* Add pardon test and documentation

Content.Server/Database/ServerUnbanDef.cs

@@ -0,0 +1,21 @@
+using System;
+using Robust.Shared.Network;
+
+namespace Content.Server.Database
+{
+    public sealed class ServerUnbanDef
+    {
+        public int BanId { get; }
+
+        public NetUserId? UnbanningAdmin { get; }
+
+        public DateTimeOffset UnbanTime { get; }
+
+        public ServerUnbanDef(int banId, NetUserId? unbanningAdmin, DateTimeOffset unbanTime)
+        {
+            BanId = banId;
+            UnbanningAdmin = unbanningAdmin;
+            UnbanTime = unbanTime;
+        }
+    }
+}