SpringBoot Configure suitable TaskExecutor for WebSocket when virtual threads are enabled

A recent issue in Spring Framework (https://github.com/spring-projects/spring-framework/issues/32081) made us aware that we overlooked websocket broker support for virtual threads.

Now that ChannelRegistration allows a plain TaskExecutor to be specified via the new executor method, it would be nice to configure it when virtual threads are enabled.

Comment From: BenchmarkingBuffalo

HI @wilkinsona, I can work on this, once spring 6.1.4 is out. You can assign it to me, if you like.

Comment From: mhalbritter

Superseded by #39611.