Add explicit example of command with env vars

What does this MR do and why?

It was pointed out in https://gitlab.com/gitlab-com/gl-infra/production/-/issues/5519#note_678393245 that sudo rejects existing env vars without the -E flag, so adding a small note and example here to recommend appending them.

A small little note, but since the collective lot of us with combined decades of sudo experience didn't notice it, maybe it's good to highlight.

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