Changes to ExecutableSchema are not reflected in federation introspection queries

### What happened?

We modify our ExecutableSchema by augmenting the Definition value of some fields based on their directives before calling `handler.New` upon it. These augmented values are not visible in the introspection query results.

It appears that the query results are being driven only by the value of the `sources` global var in the package populated by gqlgen's codegen.

### What did you expect?

We expected to be able to see such changes in the introspection query results.

### versions
- `go run github.com/99designs/gqlgen version`?

v0.17.16

- `go version`?

go version go1.19.2 darwin/arm64