docs: guide for deploying v2 after removing v1 deployment

Signed-off-by: Moritz Wanzenböck <[email protected]>

docs/how-to/upgrade/4-install-operator-v2.md

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+# Install Piraeus Operator v2
+
+After removing the Piraeus Operator v1 deployment, you can install Piraeus Operator v2.
+
+You can either use the `kubectl` method to deploy Piraeus Operator, or alternatively deploy the Operator using Helm.
+
+This is the last step when migrating Piraeus Operator from version 1 (v1) to version 2 (v2).
+[Click here to get back to the overview](./index.md).
+
+## Prerequisites
+
+* [Install `kubectl`](https://kubernetes.io/docs/tasks/tools/)
+* [Install `helm`](https://docs.helm.sh/docs/intro/install/)
+
+## Deploy Piraeus Operator v2 Using `kubectl`
+
+You can use `kubectl` and the built-in `kustomize` feature to deploy Piraeus Operator v2.
+
+First, create a file named `kustomization.yaml`, referencing the latest Piraeus Operator release, and the
+namespace you which to deploy the Piraeus Operator in. The latest releases are available  on the [release page].
+
+In the example below, the version is `v2.3.0`, and the namespace is `piraeus-datastore`.
+
+```yaml
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - https://github.com/piraeusdatastore/piraeus-operator//config/default?ref=v2.3.0 # Change the version here
+namespace: piraeus-datastore # Change the namespace here
+```
+
+Then, deploy the Operator using `kubectl` and wait for the deployment to complete:
+
+```
+$ kubectl apply -k . --server-side
+$ kubectl rollout status -n piraeus-datastore -w deploy/piraeus-operator-controller-manager
+```
+
+## Deploy Piraeus Operator v2 Using Helm
+
+To deploy Piraeus Operator v2 using Helm, clone the latest v2 release of Piraeus. The latest releases are available
+on the [release page].
+
+To also install the necessary Custom Resource Definitions for Piraeus, set `installCRDs` to `true`.
+
+```
+$ git clone -b v2.3.0 https://github.com/piraeusdatastore/piraeus-operator.git
+$ cd piraeus-operator
+$ helm install piraeus-operator charts/piraeus --set installCRDs=true
+```
+
+## Deploy the Piraeus Datastore Cluster
+
+Once the Operator is deployed, deploy the Cluster using the generated resources from [step 2](./2-collect-information.md#run-the-data-collection-script).
+
+First, create the secret used for the LINSTOR passphrase collected at the [end of step 2](./2-collect-information.md#collect-helm-generated-secrets).
+
+```
+$ cat <<-EOF | kubectl apply -f - --server-side
+apiVersion: v1
+kind: Secret
+metadata:
+  name: piraeus-op-passphrase
+  namespace: piraeus-datastore # Change the namespace here
+data:
+  MASTER_PASSPHRASE: ZVRxanl1cVBscXV1ZTk1cmEwVTk5b0ptd0F4OGFmWlVPUVA0NWNnUw==
+EOF
+```
+
+Then, apply the resource generated by the script from step 2:
+
+```
+$ kubectl apply -f v2-resources.yaml --server-side
+linstorcluster.piraeus.io/linstorcluster created
+linstorsatelliteconfiguration.piraeus.io/host-networking created
+linstorsatelliteconfiguration.piraeus.io/piraeus-op-ns created
+```
+
+Now the cluster will come up, using the existing data to restore the cluster state.
+
+## Verifying Cluster State
+
+You can check the Cluster state by using the `linstor` command line client:
+
+```
+$ kubectl exec deploy/linstor-controller -- linstor node list
+$ kubectl exec deploy/linstor-controller -- linstor storage-pool list
+$ kubectl exec deploy/linstor-controller -- linstor resource list-volumes
+$ kubectl exec deploy/linstor-controller -- linstor error-reports list
+```
+
+You can also provision new volumes, to verify that the cluster is operational.
+
+[release page]: https://github.com/piraeusdatastore/piraeus-operator/releases