feat(medusa,types): add promotion list/get endpoint (#6110)

what:

- adds get promotion endpoint (RESOLVES CORE-1677)
- adds list promotions endpoint (RESOLVES CORE-1676)
- uses new API routes

packages/types/src/promotion/service.ts

@@ -51,6 +51,12 @@ export interface IPromotionModuleService extends IModuleService {
     sharedContext?: Context
   ): Promise<PromotionDTO[]>
 
+  listAndCount(
+    filters?: FilterablePromotionProps,
+    config?: FindConfig<PromotionDTO>,
+    sharedContext?: Context
+  ): Promise<[PromotionDTO[], number]>
+
   retrieve(
     id: string,
     config?: FindConfig<PromotionDTO>,