.github/workflows/config-diff-post-comments.js: introduce "/config check ok" command

.github/workflows/config-diff-post-comments.js: introduce "/config check ok" command

Currently, we use the "Check ceph config" CI check to remind users about
any configuration changes that were detected in the PR. There's no easy
way for the script to detect if the relevant docuemtations has been
updated for the config change that was detected.

Users might get confused to still see the CI check failing even after
updating the relevant docs. We update the text message to help diffuse
the confusion. If the users will still like to see the CI check go green
- they can comment `/config check ok` and re-run the failed test.

Signed-off-by: Naveen Naidu <naveennaidu479@gmail.com>