Simplify use of DGS Codegen with GraphQlClient

[rstoyanchev]

Given schema:

type Query {
    books: [Book]
}

type Book {
    id: ID
    name: String
}

and DGS codegen generated client request types, it's possible to do this:

GraphQlClient client = HttpGraphQlClient.create(WebClient.create("http://localhost:8080/graphql"));

BooksGraphQLQuery query = new BooksGraphQLQuery();
String document = new GraphQLQueryRequest(query, new BooksProjectionRoot<>().id().name()).serialize();

List<Book> books = client.document(document)
		.retrieve(query.getOperationName())
		.toEntityList(Book.class)
		.block();

We can simplify this further through a DGS Codegen specific GraphQlClient wrapper that prepares request document, so it looks more like this:

HttpGraphQlClient httpGraphQlClient =
		HttpGraphQlClient.create(WebClient.create("http://localhost:8080/graphql"));

DgsCodegenGraphQlClient client = new DgsCodegenGraphQlClient(httpGraphQlClient);

List<Book> books = client.retrieve(new BooksGraphQLQuery(), new BooksProjectionRoot<>().id().name())
		.toEntityList(Book.class)
		.block();

This is only meant to sketch the idea, with the exact details of the API to be worked out.