Allow to auto configure `ThreadPoolTaskScheduler`/`ThreadPoolTaskExecutor` even if virtual threads enabled

[quaff]

Currently Spring Boot auto configure SimpleAsyncTaskScheduler/SimpleAsyncTaskExecutor if virtual threads enabled, so far so good.
If #42918 get merged, I suggest to introduce configuration property that allow to auto configure ThreadPoolTaskScheduler/ThreadPoolTaskExecutor instead even if virtual threads enabled.

[bclozel]

#42918 doesn't seem related, I guess you mean #42913. In any case we didn't even have time to consider the use case nor Juergen's comment, including the fact that pooling is breaking one of the best practices of virtual threads.

I've created #42921 to start discussing that with the team.