Reshaping repo

The repo is designed for use with an existing builds.sr.ht service.
Besides lacking that, I am more interested in a containerized workflow
powered by a Makefile. Package source code will live in `pkgsrc/`,
packages will be built into `pkg/`, and packaging keys will be
generated into `keys/`.

Alos trimmed the packages down to what I will build.

Add git.sr.ht-webhooks service

Fix gitsrht-migrate in git.sr.ht post-upgrade

Update git.sr.ht.post-upgrade

Add git.sr.ht package