add gitlab backup script

bin/gitlab-backup.sh

@@ -0,0 +1,9 @@
+# needs to run as root
+
+# Create a time-stamped .tar file in the current directory.
+# The .tar file will be readable only to root.
+cd /var/opt/gitlab/backups/
+sh -c 'umask 0077; tar -cf $(date "+etc-gitlab-%s.tar") -C / etc/gitlab'
+
+# run GitLab system backup, will upload to Google Cloud Storage bucket
+gitlab-rake gitlab:backup:create