Backup weekly instead of daily.

The changes are very, very rare. I'm changing the backup method to
saving tarballs as snapshots and saving the last few and this change in
the spirit of things.

crond/crontab

-@daily docker exec ldap_ldap_1 backup || wget --spider https://notify.shore.co.il/send?message=LDAP%20backup%20failed.
+@weekly docker exec ldap_ldap_1 backup || wget --spider https://notify.shore.co.il/send?message=LDAP%20backup%20failed.