SpringBoot Use virtual threads in NettyRSocketServer if enabled

Comment From: mhalbritter

Changes are in https://github.com/mhalbritter/spring-boot/tree/mh/36699-use-virtual-threads-in-nettyrsocketserver-if-enabled

Comment From: mhalbritter

We need to examine where exactly we want to have virtual threads.

Comment From: mhalbritter

We can't use virtual threads here, as this Thread is used to stop the JVM exit with the help of a non-daemon threads. This won't work with virtual threads, as they are always daemon threads and do not prevent JVM shutdown.