feat(backup.sh): add separate s3 bucket functionality for kuberesources

[eyenx]

Partially fixes #83

Sets new OCP_BACKUP_KUBERESOURCSES_S3_* variables, to push kuberesources which may contain the encrypted keys for the etcd backup (if encryption is enabled on etcd) to a separate bucket.

Only works when using S3, not yet when only using local backup folder.

See https://docs.openshift.com/container-platform/4.12/backup_and_restore/control_plane_backup_and_restore/backing-up-etcd.html

If etcd encryption is enabled, it is recommended to store this second file separately from the etcd snapshot for security reasons. However, this file is required to restore from the etcd snapshot.

[eyenx]

Not sure what the state of this is, therefore putting this on DRAFT

[tongpu]

Looks fine at first glance.

Is there a reason you switched to 4 spaces indentation or did you simply change your linter. 😛