Add premium_40GB NodeBalancer plan type (#867)

* Add `premium_40GB` NodeBalancer plan type

* typo fix

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Co-authored-by: Zhiwei Liang <[email protected]>

Author: komer3

nodebalancer.go

@@ -91,8 +91,9 @@ type NodeBalancerPlanType string
 
 // NodeBalancerPlanType constants reflect the plan type used by a NodeBalancer Config
 const (
-	NBTypePremium NodeBalancerPlanType = "premium"
-	NBTypeCommon  NodeBalancerPlanType = "common"
+	NBTypePremium     NodeBalancerPlanType = "premium"
+	NBTypePremium40GB NodeBalancerPlanType = "premium_40gb"
+	NBTypeCommon      NodeBalancerPlanType = "common"
 )
 
 // UnmarshalJSON implements the json.Unmarshaler interface