Netty ManualIoEventLoop doesn't support autoscaling

[franz1981]

netty/netty#15524 has introduced auto scaling features for SingleThreadEventExecutor including:

• the autoscaling itself
• utilization metrics

ManualIoEventLoop cannot lazily start/suspend the Thread which run it but can still:

• assign which Thread "own" it, dynamically
• if it expose as protected its states (STARTED, SHUTTING_DOWN, SHUTDOWN, TERMINATED) could be extended to both expose utilization metrics AND additional states (SUSPENDED, SUSPENDING)

I'm reporting this here because utilization metrics are very interesting and could be nicely reused and composed with "carrier" utilization metrics (still not implemented) to implements work stealing.