accept a list of Hasura types so that graphql-code-generator does not error out

[wawhal]

Actions support postgres scalars now (https://github.com/hasura/graphql-engine/pull/4333).

This causes a problem in typescript codegen because graphql-code-generator expects the SDL to be complete in itself.

Currently we have a hack to make the codegen work. The SDL is parsed and the types not found in the SDL are manually added as scalars.

A better solution would be to take Hasura scalars as an argument for the code generator.