Implement server API for handbook controls (avatar)

src/main/java/emu/grasscutter/utils/objects/HandbookBody.java

@@ -0,0 +1,23 @@
+package emu.grasscutter.utils.objects;
+
+import lombok.Builder;
+import lombok.Getter;
+
+/** HTTP request object for handbook controls. */
+public interface HandbookBody {
+    @Builder
+    class Response {
+        private int status;
+        private String message;
+    }
+
+    @Getter
+    class GrantAvatar {
+        private String player; // Parse into online player ID.
+        private String avatar; // Parse into avatar ID.
+
+        private int level = 90; // Range between 1 - 90.
+        private int constellations = 6; // Range between 0 - 6.
+        private int talentLevels = 10; // Range between 1 - 15.
+    }
+}