Discussion: Custom scalars support

[JoviDeCroock]

Summary

We need to support custom-scalars, this currently has a bit of a roadblock with regards to the schema-builder where it will expect the custom scalars to be present on the generic or it won't know how to type them. Maybe we can be clever and tell TypeScript that anything we don't know how to type should be unknown or any but that does loosen our strict-typings.

We would then need to extend the custom scalars to the configuration in our codegen, it's possible that they are automatically picked up and case to unknown but ideally the user is enabled to type these themselves.

[JoviDeCroock]

We'll probably be able to support this similar to #107 with overriding the global-type so something along the lines of BaseScalars & UserScalars.

On top of that we export some scalarType helper for folks to add their own scalars, in the docs we should document that we added JSON and DateTime for our consumers and link to common scalars like GraphQL-Scalars.

One thing that we still need to think about is how we'll integrate this with codegen, this could be a follow-up issue though, i.e. it could be part of a configuration file like the graphql-config file.

EDIT: the above becomes less of an issue with gql.tada as folks can add the types for the scalars themselves in the fuse/tada.ts file, we should ensure that we don't override this file.