Remove default replicas amount

Instead make it required to either have replicas set or max replicas.
This should ensure that users that didn't set replicas before get an
appropriate warning.

metakube/resource_node_deployment_schema.go

@@ -25,9 +25,9 @@ func metakubeResourceNodeDeploymentSpecFields() map[string]*schema.Schema {
 		"replicas": {
 			Type:          schema.TypeInt,
 			Optional:      true,
-			Default:       3,
 			Description:   "Number of replicas",
 			ConflictsWith: []string{"spec.0.min_replicas", "spec.0.max_replicas"},
+			ExactlyOneOf:  []string{"spec.0.replicas", "spec.0.max_replicas"},
 			DiffSuppressFunc: func(_, _, _ string, d *schema.ResourceData) bool {
 				minv, ok1 := d.GetOk("spec.0.min_replicas")
 				maxv, ok2 := d.GetOk("spec.0.max_replicas")