feat(backend): Add support for annual-only Billing plans

Author: dstaley

.changeset/all-readers-dream.md

@@ -1,4 +1,5 @@
 ---
+'@clerk/backend': minor
 '@clerk/localizations': minor
 '@clerk/clerk-js': minor
 '@clerk/shared': minor

packages/backend/src/api/resources/CommercePlan.ts

@@ -45,7 +45,7 @@ export class BillingPlan {
     /**
      * The monthly fee of the Plan.
      */
-    readonly fee: BillingMoneyAmount,
+    readonly fee: BillingMoneyAmount | null,
     /**
      * The annual fee of the Plan.
      */

packages/backend/src/api/resources/JSON.ts

@@ -854,7 +854,7 @@ export interface BillingPlanJSON extends ClerkResourceJSON {
   is_recurring: boolean;
   has_base_fee: boolean;
   publicly_visible: boolean;
-  fee: BillingMoneyAmountJSON;
+  fee: BillingMoneyAmountJSON | null;
   annual_fee: BillingMoneyAmountJSON | null;
   annual_monthly_fee: BillingMoneyAmountJSON | null;
   for_payer_type: 'org' | 'user';