Provide feedback to users on invalid configurations in `buf.yaml`

[doriable]

Feature

Saw a question/request around whether buf lint returns an error for invalid buf.yaml configurations, such as an incorrectly configured ignore or a stale ignore_only. We currently do not provide that feedback in buf {lint,breaking} commands.

It would be nice if either these commands can surface these issues (either as warnings or annotations) or if we had some kind of utility for validating the config, buf.yaml, e.g. a buf config subcommand, such as validate.

Some prior art worth noting: Biome provides errors on an ignore that is invalid/unnecessary.