Add ability to toggle discord rich presence

There are 3 modes: enabled, limited, and disabled.

The limited mode hides identifiable information such as username, rank, and
(if participating in one) multiplayer lobby name.

osu.Game/Overlays/Settings/Sections/Online/IntegrationSettings.cs

@@ -0,0 +1,27 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Game.Configuration;
+
+namespace osu.Game.Overlays.Settings.Sections.Online
+{
+    public class IntegrationSettings : SettingsSubsection
+    {
+        protected override string Header => "Integrations";
+
+        [BackgroundDependencyLoader]
+        private void load(OsuConfigManager config)
+        {
+            Children = new Drawable[]
+            {
+                new SettingsEnumDropdown<DiscordRichPresenceMode>
+                {
+                    LabelText = "Discord Rich Presence",
+                    Current = config.GetBindable<DiscordRichPresenceMode>(OsuSetting.DiscordRichPresence)
+                }
+            };
+        }
+    }
+}