Update generated stubs

It would be very useful to compare current schema to a set of RootResolvers (passed in as args? maybe in config?) and add any missing resolvers as stubs to the generated code.

Bonus points for dealing with conflicts.

This is a long standing idea thats been floating around since #9.

@matthewmueller mentioned https://github.com/golang/go/issues/20744 might make this tricky. Perhaps it needs to use the AST to make decisions but do the edits on the raw file bytes?