Add --force and --confirm to `ark backup delete` to support forced
backup deletion. This forcibly removes the Ark GC finalizer (if it's
present) from a backup and will orphan any resources associated with the
backup, such as backup tarballs in object storage, persistent volume
snapshots, and restores for the backup.

If a backup has a deletion timestamp, display `Deleting` in `ark backup
describe` and `ark backup get`.
Signed-off-by: Andy Goldstein <andy.goldstein@gmail.com>