WebHost: ensure correct file type for config override

[Berserker66]

What is this fixing or adding?

on prod the path to the gunicorn config file ends up in args.config_override. I don't really get why, since that's --config, not --config_override, but it does.

How was this tested?

For about two weeks on prod

Probably not the most elegant solution, but it is tested.

[qwint]

argparse.parse_known_args() will match on just a prefix so the value in --config gets matched to --config_override
https://docs.python.org/3/library/argparse.html#argparse.ArgumentParser.parse_known_args
not sure a way to turn that off though

[qwint]

looks like

parser = argparse.ArgumentParser(allow_abbrev=False)

might work instead of the workaround in this PR

[black-sliver]

The problem here is that it silently ignores some bad --config path/to/config..., so the other PR is definitely better,