cli/internal/codegen: TypeScript client has wrong type for json.RawMessage

[eandre]

Encore handles the json.RawMessage type specially and treats it as "arbitrary JSON" in generated clients.

However, the generated TypeScript client translates this to object. This is usually fine, but doesn't support arbitrary JSON values at the top level (like true or 5). We should change the generated code to using any for these types (or a more specific JSON type; see microsoft/TypeScript#1897).