Add code intelligence and CI checks for GQL queries

Created by: eseliger

Implements code intelligence on hover for gql queries in TypeScript and adds a CI check that validates that no invalid fields are used in the strings.

Depends on: https://github.com/Quramy/ts-graphql-plugin/pull/107

Errors:

Code intel:

Deprecations:

At a later stage, we can also take a look at the typegen it features, but for now wanted to get that in, which is an essential part to making integration tests safely replace e2e tests.