@UnstableApi
    public ServerBuilder serviceWorkerGroup(int numThreads) {
        virtualHostTemplate.serviceWorkerGroup(EventLoopGroups.newEventLoopGroup(numThreads), true);
        return this;
    }
Uses a newly created {@link EventLoopGroup} with the specified number of threads for
running {@link Service#serve(ServiceRequestContext, Request)}.
The worker {@link EventLoopGroup} will be shut down when the {@link Server} stops.

@param numThreads the number of event loop threads
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java