Update kubectl exec commands to include '--'

What does this MR do?

Adds a -- to kubectl exec [POD] -- [COMMAND]. If the -- is missing, a deprecation notice will be shown, but the command will still execute (for now)

kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.

Related issues

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