Interactive should rely on argparse and not its own custom logic for completions.

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-With the addition of positional arguments in our CLI it becomes more and more clear that interactive mode's completion mechanism needs to rely on argparse

-This will help replace much of the unwieldy completion code currently in interactive.

### Environment summary

Install Method (e.g. pip, interactive script, apt-get, Docker, MSI, edge build) / CLI version (`az --version`) / OS version / Shell Type (e.g. bash, cmd.exe, Bash on Windows)

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