Update to GraphiQL 2
### Feature description

Update the version of `graphiql` used to version 2

### Motivating example

This is solely a quality-of-life change that i would assign very little weight on

graphiql 2 adds dark mode, tabs, and a different UI design to graphiql 1.x

### Supporting development

I [tick all that apply]:

- [ ] am interested in building this feature myself
- [x] 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
