Add new option ignore-checks-for-mixin and deprecate ignore-mixin-members

[DanielNoord]

Current problem

What about removing ignore-members and adding a new option ignore-checks-for-mixin which would be a comma separated list of checks that exclude Mixin? We could add the supported checks to the description of that option.
I think I have already thought of good way to deprecate an option.

Originally posted by @DanielNoord in #5203 (comment)

The current ignore-mixin-members does not really convey what it is doing: disabling certain checks for mixin classes. Most notably not-async-context-manager refers to the option, which is not really clear from the option name.

Desired solution

We would like to deprecate the option and create a new option that contains a list of options that should be disabled for mixin classes.

However, deprecation of options is quite difficult with our current set-up and since we need to move to argparse anyway it might be better to wait for that change to be done first. This is thus blocked by our move to argparse.

Additional context

No response

[Pierre-Sassoulas]

Blocked by #2355 / #4455