[AT-58] Use generated Typescript types

[trevor-scheer]

This PR serves a couple purposes:

1. Get more reliable Typescript types by using code generation and CI to ensure our types stay up to date with our schema
2. Dogfood codegen (on its own codebase 😄)

TODO:

• Update CHANGELOG.md* with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

*Make sure changelog entries note which project(s) has been affected. See older entries for examples on what this looks like.