Request for adding notes for running 'helm' in Doc 'uninstall-pluggable-components'

In the third step of [Uninstall KubeSphere DevOps](https://v3-1.docs.kubesphere.io/docs/pluggable-components/uninstall-pluggable-components/)

Command 'helm' is used, but if users execut these commands directly in kubernetes cluster which 'helm' is not installed in, `-bash: helm: command not found` will be prompted. To be more frendly, I think a command, such as `kubectl exec -it ks-installer-6997c85f76-74gff -n kubesphere-system -- /bin/bash`, should be added to note users that you can run command 'helm' in ks-install

Open the linked uninstall-pluggable-components documentation and inspect its third step, where the helm commands are shown. Add a note explaining that helm may not be installed in the Kubernetes cluster and showing the mentioned kubectl exec command for entering ks-installer; the documentation should guide users to run helm successfully.

Written by the indexing model from the issue text.