transfer stabweek infrastructure to srcmgr

[markjdb]

Gleb currently owns the stabweek tagging process. He wants to hand it over, and srcmgr seems like a natural home.

First steps:

1. publish the scripts, e.g., add them to srcmgr's git repo
2. start publishing branches instead of git tags to mark stabweek branch points
3. srcmgr to own cherry-picking bug fixes into stabweek branches

Further down the road, we want to use stabweek branches to drive snapshot generation, pkgbase repos, etc..