[oryan-block]

Follow-up to #84. 15.0.0 also added GenericWrapper.withCompletionStageTransformer (#941), which #84 didn't cover.

• Schema parser options: under genericWrappers, a wrapper whose transformer returns a future of its content, like Reactor's Mono::toFuture, should be registered with withCompletionStageTransformer. A future declared inside it, like Mono<CompletableFuture<Item>>, is then waited on too. With withTransformer, graphql-java gets the inner future as the value.
• Schema parser options: dropped "Since 15.0.0" from objectMapperConfigurer / objectMapperProvider. The page describes the current version, so it just says the mapper is a Jackson 3 one.

Built it locally with Hugo 0.169.0 (same as the workflow). No errors.