SpringBoot Wrong HandlerMapping ordering for GraphQL WebSocket configuration

As of https://github.com/spring-projects/spring-framework/issues/30278, Spring Framework revisited the default ordering of the RouterFunctionMapping bean. The GraphQL WebSocket auto-configuration relied on a fixed order value for that bean so as to make the WebSocketHandlerMapping first.

We should fix the auto-configuration to make it first again and introduce a dedicated test to check for that.