[v16.x backport] doc: format doc/api/*.md with markdown formatter
Backport of https://github.com/nodejs/node/pull/40403. Current as of b83c938 in that PR. Backported from the landed commits so this is ready for review.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Backport of https://github.com/nodejs/node/pull/40403. Current as of b83c938 in that PR. Backported from the landed commits so this is ready for review.