Add --app_args support from the CLI

[tchaton]

What does this PR do?

This PR enables passing arguments to an app.py relying on Argparse.

It patches Argparse to prevent parsing verification through the parse_known_args method.

lightning run app examples/app_argparse/app.py --app_args  --use_gpu --without-server

Does your PR introduce any breaking changes? If yes, please list them.

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Did you have fun?

Make sure you had fun coding 🙃

cc @Borda

[otaj]

Now we're golden :)

[krshrimali]

LGTM 🚀 Thanks!