[CI] Consider refactoring comments into a separate workflow

[novusnota]

Currently applies only to the formatter, but some later CI checks, such as path name validations or image component checks, and the redirect checker against the upstream links could all post comments on fixing them too.

The new workflow could be triggered by:

1. The workflow_call: this will allow to separate the logic of checks from the "how to fix me" comments, effectively re-using the same commenting logic for any such needs
2. New comments from maintainers in PRs. For example, the /fmt comment, see [Format] Allow to fix the PR formatting from GitHub's UI #1006
3. Some other comments we want to check: perhaps, we can check how well the issues are opened (?) or convert PRs to drafts once they receive any review comments (more realistic scenario), etc.
4. New contributors
5. Links for all edited pages in the PR to their corresponding staging URLs
6. All possible commands, including those that are suggested in the AI workflow (/review)

Done:

• Passing checks, which should hide all prior "how to fix me" comments from the bot, see [Format] If the formatting check was successful, it should hide all prior comments from the bot and mark those as resolved #1284