Merge branch 'ds/maintenance-part-3'

Parts of "git maintenance" to ease writing crontab entries (and other scheduling system configuration) for it. * ds/maintenance-part-3: maintenance: add troubleshooting guide to docs maintenance: use 'incremental' strategy by default maintenance: create maintenance.strategy config maintenance: add start/stop subcommands maintenance: add [un]register subcommands for-each-repo: run subcommands on configured repos maintenance: add --schedule option and config maintenance: optionally skip --auto process