Migrate tools/toolsbeta grid to Debian Buster since Stretch is deprecated. This is mostly just adding Buster queues, but then Stretch queues need to go away.
[x] make sure exec grid works
[] make sure webgen grid works
[] make sure weblight grid works
[x] make sure jsub uses `stretch` as default release https://gerrit.wikimedia.org/r/plugins/gitiles/labs/toollabs/+/refs/heads/master/jobutils/bin/jsub#727
[] make sure webservice uses `stretch` as default release
[] make sure cron servers work in the new setup
[] elaborate timeline and release notes for the community in https://wikitech.wikimedia.org/wiki/News/Toolforge_Stretch_deprecation
[] make sure the release notes ask folks to migrate to k8s
[] make sure the release notes include clear information about the future of the grid