[buildifier] Feature request: CLI flag + config for globally disabling certain warnings

Right now, you can provide a list of warnings via `-warnings` or `warningsList`, but it makes it difficult to disable specific ones, as if buildifier updates you could be silently turning off all new warnings. Also, because the config file doesn't support JSONC, there's no way to annotate the file. This would improve the UX here.

I ran into this with https://github.com/bazelbuild/buildtools/issues/1492, and the easiest course of action would have been for me to just disable the one lint.

Start by tracing buildifier's existing `-warnings` and `warningsList` handling, along with its configuration-file parsing. Determine how a global disable list should interact with those existing warning selections, then add coverage for the CLI flag and configuration setting. Done means selected warnings can be disabled without suppressing newly introduced warnings.

Written by the indexing model from the issue text.