documentation: Improve the deprecation messages surrounding the GraphQLClient methods.

[berngp]

What are you missing in the docs

The @Deprecated("The RequestExecutor should be provided while creating the implementation.", ReplaceWith("Example: new DefaultGraphQLClient(url, requestExecutor);")) points toDefaultGraphQLClient, which is deprecated as well.
We need to suggest either CustomGraphQLClient, CustomReactiveGraphQLClient and WebClientGraphQLClient.

Creating a guide on when to use each of the clients mentioned above will help as well as provide examples of migrating from the deprecated method calls to the new clients.

[paulbakker]

I think the guide is already there: https://netflix.github.io/dgs/advanced/java-client/#usage

[berngp]

I think we are just missing a simple change in the GraphQLClient.kt file. Right now it reads...

graphql-dgs-client/src/main/kotlin/com/netflix/graphql/dgs/client/GraphQLClient.kt
59:    @Deprecated("The RequestExecutor should be provided while creating the implementation.", ReplaceWith("Example: new DefaultGraphQLClient(url, requestExecutor);"))
62:    @Deprecated("The RequestExecutor should be provided while creating the implementation.", ReplaceWith("Example: new DefaultGraphQLClient(url, requestExecutor);"))
116:    @Deprecated("The RequestExecutor should be provided while creating the implementation.", ReplaceWith("Example: new DefaultGraphQLClient(url, requestExecutor);"))
123:    @Deprecated("The RequestExecutor should be provided while creating the implementation.", ReplaceWith("Example: new DefaultGraphQLClient(url, requestExecutor);"))