Allow velero cli more kubectl flag access (specifically `--as` && `--as-group`)

[georgettica]

Describe the problem/challenge you have
When running the velero cli some commands require imporsonation (the --as flag) which is not exposed via the cli

Describe the solution you'd like
That the cli tooling will use the official tooling like is done here
https://github.com/dastergon/kubectl-janitor/blob/6799fcccc2ace001634e177c5e4d1805496e4276/pkg/cmd/janitor.go#L46

Anything else you would like to add:
I can contact @dastergon to help migrate to this format, but I wanted to ask your opinion before creating a PR

Environment:

N/A

This is a feature request and is currently happening on the latest version of the velero cli

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[zubron]

Hi @georgettica - Could you provide a bit more information about which commands you need to use impersonation with?

is currently happening on the latest version of the velero cli

I'm not sure what you mean by this. I'm not aware of which commands support this flag.

[georgettica]

I needed to do velero plugin add which patches the deployment
And basically any command that does k8s operations in case I need to use another user (who is elevated) to do these operations

[georgettica]

Any traction on this? @zubron