What's the problem this feature will solve?
pip is slowly getting more and more "no-warn" flags for various error messages that the user might want to silence and there are existing messages that do not have any way to silence them. It would be a good idea to simplify pip's CLI by coming up with a scalable solution to this and removing those flags.

Describe the solution you'd like
Associate string(s?) with logged messages and provide a CLI flag to allow filtering / disabling messages like --ignore-messages script-location,ssl (whatever name we land on).

Expanding on that idea, inspired by rustc --explain <code>, we could even extend that to provide explanations along with pip's error messages that can possibly go on to discuss why things are the way they are and possibly suggestions on how to fix them. This could take the form of pip help --explain <code> (I like this interface but it changes what pip help does; we can colour the bike shed later).

Alternative Solutions
None that I have explored personally.

Additional context
@cjerdonek came up with this idea and mentioned this somewhere in this issue tracker -- I can't find it now.