feat(cockpit): add new Expert plan on v1Beta1 (#2024)

Author: scaleway-bot

api/cockpit/v1beta1/cockpit_sdk.go

@@ -265,9 +265,13 @@ type PlanName string
 
 const (
 PlanNameUnknownName = PlanName("unknown_name")
-PlanNameFree = PlanName("free")
-PlanNamePremium = PlanName("premium")
-PlanNameCustom = PlanName("custom")
+// The free plan is the default plan.
+PlanNameFree = PlanName("free")
+// The premium plan with a longer retention.
+PlanNamePremium = PlanName("premium")
+PlanNameCustom = PlanName("custom")
+// The expert plan with the longest retention.
+PlanNameExpert = PlanName("expert")
 )
 
 func (enum PlanName) String() string {