build: us a shorter namespace caren-system (#662)

**What problem does this PR solve?**:
Instead of defaulting to a pretty long
`cluster-api-runtime-extensions-nutanix-system` namespace, proposing to
use a shorter name. This is similar to other CAPI providers:
```
$ kubectl get providers -A
NAMESPACE                                       NAME                            AGE   TYPE                       PROVIDER         VERSION
caaph-system                                    addon-helm                      91s   AddonProvider              helm             v0.2.1
capa-system                                     infrastructure-aws              95s   InfrastructureProvider     aws              v2.3.5
capg-system                                     infrastructure-gcp              92s   InfrastructureProvider     gcp              v1.5.0
capi-kubeadm-bootstrap-system                   bootstrap-kubeadm               96s   BootstrapProvider          kubeadm          v1.6.2
capi-kubeadm-control-plane-system               control-plane-kubeadm           96s   ControlPlaneProvider       kubeadm          v1.6.2
capi-system                                     cluster-api                     97s   CoreProvider               cluster-api      v1.6.2
cappp-system                                    infrastructure-preprovisioned   93s   InfrastructureProvider     preprovisioned   v0.21.1
capv-system                                     infrastructure-vsphere          93s   InfrastructureProvider     vsphere          v1.9.1
capvcd-system                                   infrastructure-vcd              92s   InfrastructureProvider     vcd              v1.2.0-d2iq.1
capx-system                                     infrastructure-nutanix          92s   InfrastructureProvider     nutanix          v1.4.0-alpha.2
capz-system                                     infrastructure-azure            93s   InfrastructureProvider     azure            v1.13.1-d2iq.0
caren-system                                    runtime-extension-caren         92s   RuntimeExtensionProvider   caren            v0.8.1
```

**Which issue(s) this PR fixes**:
Fixes #

**How Has This Been Tested?**:
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Author: dkoshkin

.goreleaser.yml

@@ -36,9 +36,9 @@ before:
       apiVersion: v1
       kind: Namespace
       metadata:
-        name: {{ .ProjectName }}-system
+        name: caren-system
       $(helm template {{ .ProjectName }} ./charts/{{ .ProjectName }} \
-        --namespace {{ .ProjectName }}-system \
+        --namespace caren-system \
         --set-string image.tag=v{{ trimprefix .Version "v" }} \
         {{ if .IsSnapshot }}--set-string image.repository=ko.local/{{ .ProjectName }}{{ end }} \
       )

docs/content/getting-started/deployment/via-helm.md

@@ -26,7 +26,7 @@ Add the CAREN Helm repo:
 helm repo add caren https://nutanix-cloud-native.github.io/cluster-api-runtime-extensions-nutanix/helm
 helm repo update caren
 helm upgrade --install caren caren/cluster-api-runtime-extensions-nutanix \
-  --namespace cluster-api-runtime-extensions-nutanix-system \
+  --namespace caren-system \
   --create-namespace \
   --wait \
   --wait-for-jobs