fix: authproxy CLI args parsing

[olevski]

The parsing of the CLI args and the inclusion of parameters from environment variables and config file was a bit off. Not it works as expected.

[olevski]

This change is part of the following stack:

• 758

  • 759

    • 760 ◀

_{Change managed by git-spice.}

[olevski]

@sgaist this is ready now. I noticed that the exit codes of the tests failing were not properly propagating to the github actions. So I fixed this now.