Add required-plugins config option

[notTamion]

resolves #8916 i was unsure where to add checks but i think they fit pretty nicely where they are now.

[notTamion]

i have been using the hasStarted boolean from Watchdog since that kinda behaves like a isreloading boolean. however the watchdog thread is not started until after the first tick is done. so a required plugin could have done this: and the server would not get stopped.