make gitlab backups rsyncable

tasks/backups.yml

 - name: add gitlab-rake backup cronjob
   cron:
     name: gitlab-rake backup
-    job: "/opt/gitlab/bin/gitlab-rake gitlab:backup:create CRON=1{% if gitlab.backup.disable_part %} SKIP={{ gitlab.backup.disable_part|join(',') }}{%endif%}"
+    job: "/opt/gitlab/bin/gitlab-rake gitlab:backup:create GZIP_RSYNCABLE=yes CRON=1{% if gitlab.backup.disable_part %} SKIP={{ gitlab.backup.disable_part|join(',') }}{%endif%}"
     special_time: daily
 - name: add gitlab-tar backup cronjob
   cron: