create a command to completely remove a Jenkins X installation about jx-admin

[hervelemeur]

As discovered and discussed on Slack, to avoid "not found" errors, delete first the namespaces, then the cluster:

kubectl delete -R -f config-root/namespaces
kubectl delete -R -f config-root/cluster

[jenkins-x-bot]

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/lifecycle stale

[jenkins-x-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
Rotten issues close after an additional 30d of inactivity.
If this issue is safe to close now please do so with /close.
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/lifecycle rotten

[msvticket]

I think is simple enough to issue the commands above as is also described in https://jenkins-x.io/v3/admin/uninstall/delete-jx/

So I think this issue can be closed.