Ability to supply a different GraphQL java based upon the request context.

[NavidMitchell]

Motivation:

I need to use a different GraphQL java object to process each request. This is because I currently am providing a different GraphQL schema based on a path parameter that is configured for my handler.

Ex:

        GraphQLProvider graphQlProvider = new GraphQlProvider();
        router.post(properties.getGraphqlPath()+":"+NAMESPACE_PATH_PARAMETER)
              .consumes("application/json")
              .consumes("application/graphql")
              .produces("application/json")
              .handler(BodyHandler.create(false)
                                  .setBodyLimit(properties.getMaxHttpBodySize()))
              .handler(new GqlHandler(graphQlProvider));

The design I used in the commits is probably not the cleanest. Maybe the GraphQL Provider Function should be added with a fluent method like the queryContext ext. I am not sure what makes the most sense, since the GraphQL object is currently a constructor parameter. I can change the code to whatever the Vertx team wants. But I wanted to make sure there was interest in supporting this before spending too much time.