meta: consolidate duplicate AUTHORS entries for hassaanp

Create a .mailmap entry to consolidate the two AUTHORS entries for
hassaanp into a single entry.

PR-URL: https://github.com/nodejs/node/pull/40391


Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>