Suport Java Generics

[velias]

Based on work in smallrye/smallrye-graphql#281 we should add support for java Generics into this spec.

There is a ticket discussing Generics directly in GraphQL spec graphql/graphql-spec#190. They are not there (and some of the spec authors says that intentionally), and it is question if they will ever be. We can still add it into Microprofile spec by allowing only generics with exactly defined types (no any wildchars) in the in/out object trees, and generating GraphQL schema in a way it contains extra class for each exact variant of the generic with concrete resolved types.

[beikov]

What is the status of this? I really need this!

[andymc12]

@beikov The plan is to "prove it out" in an implementation first (@velias is working it in the SmallRye implementation) and then eventually add it to the spec. This feature has not yet been targeted to a specific future release.