feature: support adding comments

[xsahil03x]

Currently there isn't any method to add or update comments in a yaml file.

Usecase: we currently use a script to update dependencies in our flutter projects, We also want to append comments to it showcasing that it's AutoGenerated and should not be modified by hand. invertase/melos#692

A similar approach is being used in Flutter repo: https://github.com/flutter/flutter/blob/master/packages/flutter/pubspec.yaml#L33-L49

[jonasfj]

I think this could cool, maybe just adding comment at the end of line for keys in a map.

But even this is really hard to express.

What happens if a map is flow mode, instead of blockmode? What if there is already a comment there?

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To be clear, if someone wants to work on this, I'd be happy to help with reviews.
I think should could be a really cool feature to have.

But it's also a feature that would need limitations and LOTS of tests 🤣