Establish a policy in case of aports developer inactivity

vaguely inspired by https://wiki.gentoo.org/wiki/Project:Retirement:

Inactivity retirement. Happens after roughly 12-16 months of inactivity and four warning mails. The exact timeline and process depends on the developer's prior activity and current situation.

currently we have 24 members of the Developers team. of those, 5 haven't been seen since 2020, some spanning all the way back to 2018, and one not having any recorded activity since the migration to GitLab; and yet, they hold full commit rights to aports, and could push changes at any time