Replace deprecated datacenter by location for priamry-ips

Hetzner has changed it's API and removed the field `datacenter` from the
primary IPs in favor of `location`. This change reflex this and adjusts
the configuration accordingly. Note, that this change didn't require any
manual state changes. Instead I applied the former plan with the newest
provider once. Hence the provider already treated the fields correctly I
only had to adjust the configuration.
Chapeau Hetzner for this good transition!

See-also: 14da745f Update tofu-resources to their latest versions
Reference: https://docs.hetzner.cloud/changelog#2025-12-16-phasing-out-datacenters

config.auto.tfvars.tpl

@@ -3,7 +3,7 @@ hetzner_cloud_apitoken = "YOUR_HETZNER_CLOUD_API_TOKEN"
 
 # Hetzner-locations: https://docs.hetzner.com/cloud/general/locations/
 k8s_servers = [
-  { type = "cax11", location = "fsn1", ip_datacenter = "fsn1-dc14" }
+  { type = "cax11", location = "fsn1" }
 ]
 k8s_agents = [
   { type = "cax11", location = "fsn1" }