Add multi-cluster CLI GitOps example

samples/multi-cluster-cli-gitops/README.md

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+# Multi-Cluster CLI GitOps Samples
+
+This is an example of using the `multi-cluster-cli` in a [GitOps](https://www.weave.works/technologies/gitops/) operating model to perform a recovery of the dataplane
+in a multi-cluster deployment scenario. For more details on managing multi-cluster resources with the kubernetes operator see [the official documentation](https://www.mongodb.com/docs/kubernetes-operator/master/multi-cluster/). The example is applicable for an [ArgoCD](https://argo-cd.readthedocs.io/) configuration.
+
+## ArgoCD configuration
+The files in the [argocd](./argocd) contain an [AppProject](./argocd/project.yaml) and an [Application](./argocd/application.yaml) linked to it which allows the synchronization of `MongoDBMulti` resources from a Git repo.
+
+## Multi-Cluster CLI Job setup
+To enable the manual disaster recovery using the CLI, this sample provides a [Job](./resources/job.yaml) which runs the recovery subcommand as a [PreSync hook](https://argo-cd.readthedocs.io/en/stable/user-guide/resource_hooks/). This ensures that the multicluster environment is configured before the application of the modified [`MongoDBMulti`](./resources/replica-set.yaml) resource. The `Job` mounts the same `kubeconfig` that the operator is using to connect to the clusters defined in your architecture. 
+
+### Build the multi-cluster CLI image
+You can build a minimal image containing the CLI executable using the `Dockerfile` [provided in this repo](./../../tools/multicluster/Dockerfile).
+``` shell
+git clone https://github.com/mongodb/mongodb-enterprise-kubernetes
+cd mongodb-enterprise-kubernetes/tools/multicluster
+docker build . -t "your-registry/multi-cluster-cli:latest"
+docker push "your-registry/multi-cluster-cli:latest"
+```

samples/multi-cluster-cli-gitops/argocd/application.yaml

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+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: multi-cluster-replica-set
+  namespace: argocd
+  finalizers:
+    - resources-finalizer.argocd.argoproj.io
+  labels:
+    name: database
+spec:
+  project: my-project
+  source:
+    repoURL: https://github.com/mongodb/mongodb-enterprise-kubernetes
+    targetRevision: "fix/ubi-8-repo-names"
+    path: samples/multi-cluster-cli-gitops
+  destination:
+    server: https://central.mongokubernetes.com
+    namespace: mongodb
+  syncPolicy:
+    automated:
+      prune: true
+    syncOptions:
+    - CreateNamespace=true

samples/multi-cluster-cli-gitops/argocd/project.yaml

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+apiVersion: argoproj.io/v1alpha1
+kind: AppProject
+metadata:
+  name: my-project
+  namespace: argocd
+  finalizers:
+    - resources-finalizer.argocd.argoproj.io
+spec:
+  description: Example Project
+  sourceRepos:
+  - '*'
+  destinations:
+  - namespace: mongodb
+    server: https://central.mongokubernetes.com
+  clusterResourceWhitelist:
+  # Allow MongoDBMulti resources to be synced
+  - group: ''
+    kind: MongoDBMulti
+  # Allow Jobs to be created (used for sync hooks in this example)
+  - group: ''
+    kind: Job
+  - group: ''
+    kind: Namespace

samples/multi-cluster-cli-gitops/resources/job.yaml

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+# Sample PreSync job to perform the manual dataplane recovery before a replica set sync
+---
+apiVersion: batch/v1
+kind: Job
+metadata:
+  generateName: multicluster-cli-recover-
+  annotations:
+    argocd.argoproj.io/hook: PreSync
+    argocd.argoproj.io/hook-delete-policy: HookSucceeded
+spec:
+  template:
+    spec:
+      containers:
+      - name: multicluster-cli
+        image: your-registry/multi-cluster-cli
+        env:
+        - name: KUBECONFIG
+          value: /etc/config/kubeconfig
+        args:
+        - "-central-cluster=central.mongokubernetes.com"
+        - "-member-clusters=cluster1.mongokubernetes.com,cluster2.mongokubernetes.com,cluster4.mongokubernetes.com"
+        - "-member-cluster-namespace=mongodb"
+        - "-central-cluster-namespace=mongodb"
+        - "-operator-name=mongodb-enterprise-operator-multi-cluster"
+        - "-source-cluster=cluster1.mongokubernetes.com"
+        volumeMounts:
+        - mountPath: /etc/config/kubeconfig
+          name: kube-config-volume
+      restartPolicy: Never
+      volumes:
+      - name: kube-config-volume
+        secret:
+          defaultMode: 420
+          secretName: mongodb-enterprise-operator-multi-cluster-kubeconfig
+
+  backoffLimit: 2

samples/multi-cluster-cli-gitops/resources/replica-set.yaml

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+# sample mongodb-multi replicaset yaml
+---
+apiVersion: mongodb.com/v1
+kind: MongoDBMulti
+metadata:
+  name: multi-replica-set
+spec:
+  version: 4.4.0-ent
+  type: ReplicaSet
+  persistent: false
+  duplicateServiceObjects: false
+  credentials: my-credentials
+  opsManager:
+    configMapRef:
+      name: my-project
+  clusterSpecList:
+    # provide spec per cluster
+    clusterSpecs:
+        # cluster names where you want to deploy the replicaset
+      - clusterName: cluster1.mongokubernetes.com
+        members: 2
+      - clusterName: cluster2.mongokubernetes.com
+        members: 1
+      - clusterName: cluster4.mongokubernetes.com
+        members: 2