[Feature] CubeOptions need validation

[weilaaa]

Why CubeOptions need validation?
Before running KubeCube, we are supposed to doing options validate, quick exit if validate failed.

	Start = func(c *cli.Context) error {
		if errs := flags.CubeOpts.Validate(); len(errs) > 0 {
			return utilerrors.NewAggregate(errs)
		}

		run(flags.CubeOpts, signals.SetupSignalHandler())

		return nil
	}

How to do it?
We had validate method but in fact doing nothing in each validate func, we need complete it.

// Validate verify options for every component
// todo(weilaaa): complete it
func (s *CubeOptions) Validate() []error {
	var errs []error

	errs = append(errs, s.APIServerOpts.Validate()...)
	errs = append(errs, s.ClientMgrOpts.Validate()...)
	errs = append(errs, s.CtrlMgrOpts.Validate()...)

	return errs
}

func (c *Config) Validate() []error {
	return nil
}