Move ClientSet and utilities to another repo

[MartinForReal]

Is your feature request related to a problem? Please describe.
I don't want to add unused dependencies such as client-go and etc when I use controller-runtime to develop operators.

Describe the solution you'd like
I think it would be a good idea to move pkg/clientset and pkg/apis/helpers to another repo such as volcano/client-go like what istio/client-go did.

Additional context
There is no need to add replace statement in go.mod

[Thor-wl]

Sounds reasonable. Thanks for youre advice. I'll take it.
/assign @Thor-wl