chore: create `funding.json` (#3919)

### Description
- Add verification for OP retro funding round 4

---------

Co-authored-by: Nam Chu Hoai <nambrot@googlemail.com>
Co-authored-by: Paul Balaji <paul@hyperlane.xyz>

funding.json

@@ -0,0 +1,5 @@
+{
+    "opRetro": {
+        "projectId": "0xa47182d330bd0c5c69b1418462f3f742099138f09bff057189cdd19676a6acd1"
+    }
+}