sleep 10 minutes before pruning backups

if pruning happens immediatley after taking the backup a race condition
can occur where a backup that would theoretically be eligible won't be
pruned as the current backup run was very fast, putting the potential
candidate just at the very edge of the selected time window

src/backup.sh

@@ -72,6 +72,7 @@ echo "Will wait for next scheduled backup."
 
 if [ ! -z "$BACKUP_RETENTION_DAYS" ]; then
   info "Pruning old backups"
+  echo "Sleeping ${BACKUP_PRUNING_LEEWAY} before checking eligibility."
   bucket=$AWS_S3_BUCKET_NAME
 
   rule_applies_to=$(mc rm --fake --recursive -force --older-than "${BACKUP_RETENTION_DAYS}d" "backup-target/$bucket" | wc -l)

src/entrypoint.sh

@@ -15,6 +15,7 @@ BACKUP_CRON_EXPRESSION="${BACKUP_CRON_EXPRESSION:-@daily}"
 BACKUP_FILENAME=${BACKUP_FILENAME:-"backup-%Y-%m-%dT%H-%M-%S.tar.gz"}
 
 BACKUP_RETENTION_DAYS="${BACKUP_RETENTION_DAYS:-}"
+BACKUP_PRUNING_LEEWAY="${BACKUP_PRUNING_LEEWAY:-10m}"
 
 AWS_S3_BUCKET_NAME="${AWS_S3_BUCKET_NAME:-}"
 AWS_ENDPOINT="${AWS_ENDPOINT:-s3.amazonaws.com}"