Update and improve Azure and LVM snapshot backups documentation
#### Overview Continuing: https://gitlab.com/gitlab-com/infrastructure/issues/28 Our backup documentation needs an overall: + [x] - Move [backup.md](https://dev.gitlab.org/cookbooks/chef-repo/blob/master/doc/backups.md) to [runbooks](https://gitlab.com/gitlab-com/runbooks) + [ ] - Include information for recovering from (local host) LVM snapshots + [ ] - Remove outdated ebs information + [ ] - Document possible issues/troubleshooting when restoring Azure snapshots (lessons learnt in https://gitlab.com/gitlab-com/infrastructure/issues/252 ) //cc @marat
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