Extensible hub addon manager by integration controller-runtime

[yue9944882]

the addon manager can also be a normal kubernetes operator in the hub cluster. it will be better if the addon-framework can help addon developers to extend the addon manager with controller behaviors. in the latest version of controller-runtime, it supports receiving external events via source.Channel and the reconcile loop receives a context which is extensible for us to plumb the target cluster name. we can have a few integration utilities that helps us to easily build a controller based on the widely-used controller-runtime.