graphql: remove shaded/harcoded gson dependency

[jknack]

Starting from 4.5.0 graphql module requires a json module:

{
   install(new Jackson3Module()); // or Jackson2Module or AvajeJsonbModule or YassonModule
   install(new GraphqlModule());
}

To keep using gson:

{
   install(new GsonModule());
   install(new GraphqlModule());
}