Ⅰ. Describe what this PR does

Added an adaptive scheduling strategy to UnitedDeployment. During scaling up, if a subset causes some Pods to be unschedulable for certain reasons, the unschedulable Pods will be rescheduled to other partitions. During scaling down, if elastic allocation is used (i.e., the subset is configured with min/max), each partition will retain the ready Pods as much as possible without exceeding the maximum capacity, rather than strictly scaling down in reverse order of the Subset list.

Ⅱ. Does this pull request fix one issue?

fixes #1673

Ⅲ. Describe how to verify it

Use the yaml below to create a UD with subset-b unschedulable.

apiVersion: apps.kruise.io/v1alpha1
kind: UnitedDeployment
metadata:
  name: sample-ud
spec:
  replicas: 5
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: sample
  template:
    deploymentTemplate:
      metadata:
        labels:
          app: sample
      spec:
        selector:
          matchLabels:
            app: sample
        template:
          metadata:
            labels:
              app: sample
          spec:
            terminationGracePeriodSeconds: 0
            containers:
              - name: nginx
                image: curlimages/curl:8.8.0
                command: ["/bin/sleep", "infinity"]
  topology:
    scheduleStrategy:
      type: Adaptive
      adaptive:
        rescheduleCriticalSeconds: 10
        unschedulableLastSeconds: 20

    subsets:
      - name: subset-a
        maxReplicas: 2
        nodeSelectorTerm:
          matchExpressions:
            - key: kubernetes.io/hostname
              operator: In
              values:
                - ci-testing-worker
      - name: subset-b
        maxReplicas: 2
        nodeSelectorTerm:
          matchExpressions:
            - key: kubernetes.io/hostname
              operator: In
              values:
                - not-exist
      - name: subset-c
        nodeSelectorTerm:
          matchExpressions:
            - key: kubernetes.io/hostname
              operator: In
              values:
                - ci-testing-worker3

1. when created, two pods in subset-b will stay pending
2. after 10s, the two pending pods will be rescheduled to subset-c
3. scale up immediately, new pods will be created in subset-c instead of subset-b (even not full)
4. wait 20s, when subset-b is recovered, scale up again, 2 pods will be scheduled into subset-b again (and still pending)
5. whenever you scale down:
   subset-c -> subset-b -> subset-a

Ⅳ. Special notes for reviews

1. adapter.go: GetReplicaDetails returns pods in the subset
2. xxx_adapter.go: return pods implementation ⬆️
3. allocator.go: about safeReplica
4. pod_condition_utils.go: extract PodUnscheduledTimeout function from workloadwpread
5. reschedule.go: PodUnscheduledTimeout function extracted
6. subset.go: add some field to Subset object to carry related information
7. subset_control.go: store subset pods to Subset object
8. uniteddeployment_controller.go
   1. add requeue feature to check failed pods
   2. subset unschedulable status management
9. uniteddeployment_types.go: API change
10. uniteddeployment_update.go: sync unschedulable to CR