Make errors 27 and 32 non-fatal by default

[lessp]

I see this hinder newcomers quite often, and I'd argue that it be a smoother onboarding experience if these were only warnings by default. What do you think?

https://dune.readthedocs.io/en/stable/faq.html#how-to-turn-specific-errors-into-warnings

[Leonidas-from-XIV]

The problem is that warnings at the moment are quite useless in Dune as Dune has no way to replay warnings (as we'd want to display warnings of files that successfully built, otherwise the user won't see them at all). I'd suggest first implementing a mechanism to store and replay warnings which would open the door to a lot of potential improvements regarding warnings and errors.