Remove lock ttl from the kured defaults

[valkenburg-prevue-ch]

https://github.com/kube-hetzner/terraform-hcloud-kube-hetzner/blame/8cb5c3e3054530da6f4d4af640d2200b6eb701bc/locals.tf#L624

IMHO this is a regression: the ttl makes the lock expire when a node is cordoned and fails to complete the reboot cycle. As a consequence, it is possible the one by one many nodes become unavailable, practically taking down the cluster. I had to understand this the hard way. I would prefer the default being what it was before, no lock expiration. We could expand the comment about kured_options in kube.tf.example maybe?

[mysticaltech]

Merged, will do a release later today.