Move system updates to the same patch system as members

PluralKit.Core/Models/Patch/SystemPatch.cs

@@ -0,0 +1,31 @@
+#nullable enable
+namespace PluralKit.Core
+{
+    public class SystemPatch: PatchObject
+    {
+        public Partial<string?> Name { get; set; }
+        public Partial<string?> Description { get; set; }
+        public Partial<string?> Tag { get; set; }
+        public Partial<string?> AvatarUrl { get; set; }
+        public Partial<string?> Token { get; set; }
+        public Partial<string> UiTz { get; set; }
+        public Partial<PrivacyLevel> DescriptionPrivacy { get; set; }
+        public Partial<PrivacyLevel> MemberListPrivacy { get; set; }
+        public Partial<PrivacyLevel> FrontPrivacy { get; set; }
+        public Partial<PrivacyLevel> FrontHistoryPrivacy { get; set; }
+        public Partial<bool> PingsEnabled { get; set; }
+
+        public override UpdateQueryBuilder Apply(UpdateQueryBuilder b) => b
+            .With("name", Name)
+            .With("description", Description)
+            .With("tag", Tag)
+            .With("avatar_url", AvatarUrl)
+            .With("token", Token)
+            .With("ui_tz", UiTz)
+            .With("description_privacy", DescriptionPrivacy)
+            .With("member_list_privacy", MemberListPrivacy)
+            .With("front_privacy", FrontPrivacy)
+            .With("front_history_privacy", FrontHistoryPrivacy)
+            .With("pings_enabled", PingsEnabled);
+    }
+}