Add permission for buildbucket reader

Without this buildbucket cannot read our config/recipes

Release-Notes: skip
Change-Id: I67b6b94b3cd520682c7755eaed162d284eac0ec7
diff --git a/main.star b/main.star
index 4958be1..0cda51b 100755
--- a/main.star
+++ b/main.star
@@ -42,6 +42,12 @@
             roles = "role/configs.developer",
             groups = "googlers",
         )
+
+        # Allow buildbucket to read config and recipes.
+        luci.binding(
+            roles = "role/buildbucket.reader",
+            groups = "all",
+        )
     ],
 )