What would you like to be added:
I'd like to add the Partition field to RollingUpdateConfiguration struct like sts.

// leaderworkerset_types.go
type RollingUpdateConfiguration struct {
        Partition *int32

	MaxUnavailable intstr.IntOrString `json:"maxUnavailable,omitempty"`

	MaxSurge intstr.IntOrString `json:"maxSurge,omitempty"`
}

Meanwhile, the rollingUpdateParameters function in lws controller also needs to be restructured to add the partition update feature.

Why is this needed:
It enable lws to have the ability to perform partitioned updates. This is helpful in being able to do a canary based deployment.

Completion requirements:

This enhancement requires the following artifacts:

• Design doc
• API change
• Docs update

The artifacts should be linked in subsequent comments.