[red-knot] Support --exit-zero and --error-on-warning

[InSyncWithFoo]

Summary

Resolves #15500, resolves #15501.

Red Knot now accepts --exit-zero and --error-on-warning as CLI flags. The following table summarizes their effect on the exit code:

Output	No errors	At least one warning	At least one error	Panic
Default	0	0	1	2
--exit-zero	0	0	0	2
--error-on-warning	0	1	1	2

Test Plan

Unit tests.

[MichaReiser]

Thanks. We can't use self.cli_options in main_loop. We instead need to use project.options (ideally settings) to respect the same value being set in a configuration file.

[MichaReiser]

Thanks, this is great.

I decided to revert the Options changes again and add configuration support as part of https://github.com/astral-sh/ruff/issues/15491. The reason I reverted is mainly that we shouldn't use Options outside the "reading and merging the configuration" phase. We should introduce a dedicated Settings struct, similar to what we have in Ruff, that stores the resolved Options (with defaults filled in)