GraphQL 16 support
### Feature description

postgraphile requires `graphql` version 15 or lower. Since graphql 16 has been stable for a while, I'd love to see it being supported by postgraphile.

### Supporting development

I [tick all that apply]:

<!-- To tick a checkbox, change it from `[ ]` to `[x]` -->

- [ ] am interested in building this feature myself
- [ ] am interested in collaborating on building this feature
- [x] am willing to help testing this feature before it's released
- [ ] am willing to write a test-driven test suite for this feature (before it exists)
- [ ] am a [Graphile sponsor](https://www.graphile.org/sponsor/) ❤️
- [ ] have an active [support or consultancy contract](https://www.graphile.org/support/) with Graphile
