doc: add entry for `AsyncHook` class

fixes: https://github.com/nodejs/node/issues/31661

PR-URL: https://github.com/nodejs/node/pull/31865
Fixes: https://github.com/nodejs/node/issues/31661


Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>