Migrate guild objects to the patch system

PluralKit.Core/Models/Patch/SystemGuildPatch.cs

@@ -0,0 +1,15 @@
+#nullable enable
+namespace PluralKit.Core
+{
+    public class SystemGuildPatch: PatchObject
+    {
+        public Partial<bool> ProxyEnabled { get; set; }
+        public Partial<AutoproxyMode> AutoproxyMode { get; set; }
+        public Partial<MemberId?> AutoproxyMember { get; set; }
+
+        public override UpdateQueryBuilder Apply(UpdateQueryBuilder b) => b
+            .With("proxy_enabled", ProxyEnabled)
+            .With("autoproxy_mode", AutoproxyMode)
+            .With("autoproxy_member", AutoproxyMember);
+    }
+}