Fix small issues with wundergraph_cli

[weiznich]

Sometimes the generated file contains structs which may contain types (for example uuid::Uuid or chrono::DateTime) that are nowt in the prelude. wundergraph_cli does nto generate the required imports there. Find a way to do that.
I think the easiest way to fix that is to just generate fully qualified paths instead of using only the type name there. Type mapping is happening here

[naufraghi]

I can work on this