support partition in rollingupdate

[gujingit]

Ⅰ. Motivation

Support rollingUpdate with partition. This is helpful in incremental rollout strategies like canary deployments or interactive rollout strategies for multiple replicas like xPyD deployments.

Ⅱ. Modifications

type RollingUpdate struct {
        // add partition configuration
	Partition      *int32             `json:"partition,omitempty"`
	MaxUnavailable intstr.IntOrString `json:"maxUnavailable,omitempty"`
	MaxSurge       intstr.IntOrString `json:"maxSurge,omitempty"`
}

Ⅲ. Does this pull request fix one issue?

None

Ⅳ. List the added test cases (unit test/integration test) if any, please explain if no tests are needed.

TestLeaderWorkerSetReconciler_Reconciler()
TestStatefulSetReconciler_Reconciler()

Ⅴ. Describe how to verify it

follow the update-strategy.md

VI. Special notes for reviews

Checklist

• Format your code make fmt.
• Add unit tests or integration tests.
• Update the documentation related to the change.

[cheyang]

/lgtm
/approve

[cheyang]

/lgtm
/approve