ENH Add `.graphql-generated` directory by default.

This directory will be required for all new projects (unless explicitly
opting out of graphql v4) - having this directory by default makes it
easier to set more sane permissions (i.e. not requiring the entire
project root to be writable).

composer.json

@@ -15,7 +15,8 @@
     "extra": {
         "project-files": [
             "app/_config/*",
-            ".env.example"
+            ".env.example",
+            ".graphql-generated/*"
         ],
         "public-files": [
             "assets/*",