public Server start() {
        return delegate.start();
    }
Starts the {@link Server} configured by {@link #configure(ServerBuilder)}.
If the {@link Server} has been started up already, the existing {@link Server} is returned.
Note that this operation blocks until the {@link Server} finished the start-up.

@return the started {@link Server}
junit5/src/main/java/com/linecorp/armeria/testing/junit5/server/ServerExtension.java