upcloud: add server groups and target port for lb (#9831)

contrib/terraform/upcloud/sample-inventory/cluster.tfvars

@@ -122,6 +122,7 @@ loadbalancer_plan = "development"
 loadbalancers = {
   # "http" : {
   #   "port" : 80,
+  #   "target_port" : 80,
   #   "backend_servers" : [
   #     "worker-0",
   #     "worker-1",
@@ -129,3 +130,20 @@ loadbalancers = {
   #   ]
   # }
 }
+
+server_groups = {
+  # "control-plane" = {
+  #   servers = [
+  #     "master-0"
+  #   ]
+  #   anti_affinity = true
+  # },
+  # "workers" = {
+  #   servers = [
+  #     "worker-0",
+  #     "worker-1",
+  #     "worker-2"
+  #   ]
+  #   anti_affinity = true
+  # }
+}