Add cluster-api solution (#78)

* Add cluster-api solution

Signed-off-by: Jian Qiu <jqiu@redhat.com>

* Resolve comments

Signed-off-by: Jian Qiu <jqiu@redhat.com>

Signed-off-by: Jian Qiu <jqiu@redhat.com>

solutions/cluster-api/README.md

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+# Working with the Cluster API project
+
+[Cluster API](https://cluster-api.sigs.k8s.io/) is a Kubernetes sub-project focused on providing declarative APIs and
+tooling to simplify provisioning, upgrading, and operating multiple Kubernetes clusters. This doc is a guideline on how
+to use the Cluster API project and the [Open Cluster Management (OCM)](https://open-cluster-management.io/) project together.
+
+## Prerequisite
+Download and install [clusteradm](https://github.com/open-cluster-management-io/clusteradm/releases). For Linux OS, run the following commands:
+
+```shell
+wget -qO- https://github.com/open-cluster-management-io/clusteradm/releases/latest/download/clusteradm_linux_amd64.tar.gz | sudo tar -xvz -C /usr/local/bin/
+
+sudo chmod +x /usr/local/bin/clusteradm
+```
+
+Follow the instruction [here](https://cluster-api.sigs.k8s.io/user/quick-start.html) to install the `clusterctl`.
+
+## Initialize the Cluster API management plane and create a cluster
+
+Before initilize the management plane, some feature gates should be enabled:
+
+```shell
+export CLUSTER_TOPOLOGY=true
+export EXP_CLUSTER_RESOURCE_SET=true
+```
+
+Next initiate the Cluster API management plane by following [this](https://cluster-api.sigs.k8s.io/user/quick-start.html#initialize-the-management-cluster)
+
+Now create a cluster on any cloud provider by following the instruction [here](https://cluster-api.sigs.k8s.io/user/quick-start.html#create-your-first-workload-cluster).
+
+## Initialize the OCM multicluster control plane hub cluster and register the newly created cluster
+
+The OCM multicluster control plane hub can be run in the same cluster as the Cluster API management plane. Use the following command to initialize the hub cluster: 
+
+```
+clusteradm init --use-bootstrap-token
+```
+
+Register the newly created cluster by running the following command:
+
+```
+./register-join.sh <cluster-name> # ./register-join.sh capi-cluster
+```
+
+The registration process might take a while. After it's done, you can run the following command to verify the newly created cluster has successfully joined the hub cluster:
+
+```
+kubectl get managedcluster
+```

solutions/cluster-api/register-join.sh

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+#!/bin/bash
+
+cd $(dirname ${BASH_SOURCE})
+
+set -e
+
+CLUSTER_NAME=$1
+
+echo "get bootstrap token from ocm hub cluster"
+joincmd=$(clusteradm get token --use-bootstrap-token | grep clusteradm)
+
+echo "Join $1 to hub"
+$(echo ${joincmd} --dry-run --output-file join.yaml  | sed "s/<cluster_name>/$CLUSTER_NAME/g")
+kubectl create secret generic import-secret-$1 --from-file=join.yaml --type=addons.cluster.x-k8s.io/resource-set
+
+cat << EOF | kubectl apply -f -
+apiVersion: addons.cluster.x-k8s.io/v1alpha3
+kind: ClusterResourceSet
+metadata:
+ name: import-$CLUSTER_NAME
+spec:
+ strategy: "ApplyOnce"
+ clusterSelector:
+   matchLabels:
+     cluster.x-k8s.io/cluster-name: $CLUSTER_NAME
+ resources:
+   - name: import-secret
+     kind: Secret
+EOF