Add a CRD sample

Signed-off-by: chaunceyjiang <chaunceyjiang@gmail.com>

samples/guestbook/README.md

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+# Propagate CRD application
+The following steps demonstrating how to propagate a [Guestbook](https://book.kubebuilder.io/quick-start.html#create-a-project) which is defined by CRD.
+
+Assume you are under the guestbook directory.
+```bash
+cd samples/guestbook
+```
+and set the KUBECONFIG environment with Karmada configuration.
+```bash
+export KUBECONFIG=${HOME}/.kube/karmada.config
+```
+1. Create Guestbook CRD in Karmada
+```bash
+kubectl apply -f guestbooks-crd.yaml 
+``` 
+The CRD should be applied to `karmada-apiserver`.
+2. Create ClusterPropagationPolicy that will propagate Guestbook CRD to member cluster
+```bash
+kubectl apply -f guestbooks-clusterpropagationolicy.yaml
+```
+The CRD will be propagated to member clusters according to the rules defined in ClusterPropagationPolicy
+>Note: We can only use ClusterPropagationPolicy not PropagationPolicy here.
+> Please refer to FAQ Difference between [PropagationPolicy and ClusterPropagationPolicy](https://github.com/karmada-io/karmada/blob/master/docs/frequently-asked-questions.md#what-is-the-difference-between-propagationpolicy-and-clusterpropagationpolicy)
+> for more details.
+3. Create a Guestbook named `guestbook-sample` in Karmada
+```bash
+kubectl apply -f guestbook.yaml
+```
+4. Create PropagationPolicy that will propagate `guestbook-sample` to member cluster
+```bash 
+kubectl apply -f guestbooks-propagationpolicy.yaml
+```
+5. Check the `guestbook-sample` status from Karmada
+```bash
+kubectl get guestbook -oyaml
+```
+6. Create OverridePolicy that will override the size field of guestbook-sample in member cluster
+```bash
+kubectl apply -f guestbooks-overridepolicy.yaml
+```
+7. Check the size field of `guestbook-sample` from member cluster
+```bash
+kubectl --kubeconfig=${HOME}/.kube/members.config config use-context member1
+kubectl --kubeconfig=${HOME}/.kube/members.config get guestbooks -o yaml
+```
+If it works as expected, the `.spec.size` will be overwritten to `4`.

samples/guestbook/guestbook.yaml

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+apiVersion: webapp.my.domain/v1
+kind: Guestbook
+metadata:
+  name: guestbook-sample
+spec:
+  size: 2
+  configMapName: test
+  alias: Name

samples/guestbook/guestbooks-clusterpropagationolicy.yaml

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+# propagationpolicy.yaml
+apiVersion: policy.karmada.io/v1alpha1
+kind: ClusterPropagationPolicy
+metadata:
+  name: example-policy # The default namespace is `default`.
+spec:
+  resourceSelectors:
+    - apiVersion: apiextensions.k8s.io/v1
+      kind: CustomResourceDefinition
+      name: guestbooks.webapp.my.domain
+  placement:
+    clusterAffinity:
+      clusterNames:
+        - member1

samples/guestbook/guestbooks-crd.yaml

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+apiVersion: apiextensions.k8s.io/v1
+kind: CustomResourceDefinition
+metadata:
+  annotations:
+    controller-gen.kubebuilder.io/version: v0.8.0
+  creationTimestamp: null
+  name: guestbooks.webapp.my.domain
+spec:
+  group: webapp.my.domain
+  names:
+    kind: Guestbook
+    listKind: GuestbookList
+    plural: guestbooks
+    singular: guestbook
+  scope: Namespaced
+  versions:
+  - name: v1
+    schema:
+      openAPIV3Schema:
+        description: Guestbook is the Schema for the guestbooks API
+        properties:
+          apiVersion:
+            description: 'APIVersion defines the versioned schema of this representation
+              of an object. Servers should convert recognized schemas to the latest
+              internal value, and may reject unrecognized values. More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources'
+            type: string
+          kind:
+            description: 'Kind is a string value representing the REST resource this
+              object represents. Servers may infer this from the endpoint the client
+              submits requests to. Cannot be updated. In CamelCase. More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds'
+            type: string
+          metadata:
+            type: object
+          spec:
+            description: GuestbookSpec defines the desired state of Guestbook
+            properties:
+              alias:
+                enum:
+                - Phone
+                - Address
+                - Name
+                type: string
+              configMapName:
+                description: Name of the ConfigMap for GuestbookSpec's configuration
+                maxLength: 15
+                minLength: 1
+                type: string
+              size:
+                description: Quantity of instances
+                format: int32
+                maximum: 10
+                minimum: 1
+                type: integer
+            required:
+            - configMapName
+            - size
+            type: object
+          status:
+            description: GuestbookStatus defines the observed state of Guestbook
+            properties:
+              active:
+                description: PodName of the active Guestbook node.
+                type: string
+              standby:
+                description: PodNames of the standby Guestbook nodes.
+                items:
+                  type: string
+                type: array
+            required:
+            - active
+            - standby
+            type: object
+        type: object
+    served: true
+    storage: true
+    subresources:
+      status: {}
+status:
+  acceptedNames:
+    kind: ""
+    plural: ""
+  conditions: []
+  storedVersions: []

samples/guestbook/guestbooks-overridepolicy.yaml

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+apiVersion: policy.karmada.io/v1alpha1
+kind: OverridePolicy
+metadata:
+  name: guestbook-sample
+spec: 
+  resourceSelectors: 
+  - apiVersion: webapp.my.domain/v1 
+    kind: Guestbook
+  overrideRules: 
+  - targetCluster: 
+      clusterNames:
+      - member1
+    overriders:
+      plaintext:
+      - path: /spec/size
+        operator: replace
+        value: 4
+      - path: /metadata/annotations
+        operator: add
+        value: {"OverridePolicy":"test"}

samples/guestbook/guestbooks-propagationpolicy.yaml

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+apiVersion: policy.karmada.io/v1alpha1
+kind: PropagationPolicy
+metadata:
+  name: example-policy
+spec:
+  resourceSelectors:
+    - apiVersion: webapp.my.domain/v1
+      kind: Guestbook
+  placement:
+    clusterAffinity:
+      clusterNames:
+        - member1