The way the eZ Platform GraphQL schema is generated at this time makes it difficult to mix the generated schema with an independent one that would use the same graphql library, for instance to expose custom doctrine entities.

Allow integrators to create a custom `app/config/graphql/Query.types.yml` file that gets used as the schema root if it exists. Note that it must either inherit the eZ Platform schema (inheritance), or expose it from one of its fields (composition).