aptly: Add snapshot policy script

The `bs_aptly_snapshot_policy` script run snapshot retention policies.
Each snapshot retention policy is defined by a YAML file, stored by
default at `/srv/obs/aptly/snapshot.policy.d/`.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>
4 jobs for wip/adalessandro/aptly-snapshot-policy in 27 minutes and 21 seconds (queued for 3 seconds)