chore: add funding.json for op grant (#1608)

funding.json

@@ -0,0 +1,5 @@
+{
+  "opRetro": {
+    "projectId": "0x892cf9449b4046f9b68efe6ffccfcd8df1322b1a9ffc65a2bbfe1207c4ceba8d"
+  }
+}