feat(core-flows,types,medusa): API to add promotions to campaign (#7277)

what:

- adds an API to add promotions to campaign
- reworks module to perform atomic actions

packages/modules/promotion/src/models/campaign.ts

@@ -70,9 +70,7 @@ export default class Campaign {
   })
   budget: CampaignBudget | null = null
 
-  @OneToMany(() => Promotion, (promotion) => promotion.campaign, {
-    orphanRemoval: true,
-  })
+  @OneToMany(() => Promotion, (promotion) => promotion.campaign)
   promotions = new Collection<Promotion>(this)
 
   @Property({

packages/modules/promotion/src/models/promotion.ts

@@ -45,13 +45,17 @@ export default class Promotion {
   })
   code: string
 
-  @Searchable()
   @ManyToOne(() => Campaign, {
+    columnType: "text",
     fieldName: "campaign_id",
     nullable: true,
-    cascade: ["soft-remove"] as any,
+    mapToPk: true,
+    onDelete: "set null",
   })
-  campaign: Campaign | null = null
+  campaign_id: string | null = null
+
+  @ManyToOne(() => Campaign, { persist: false })
+  campaign: Campaign | null
 
   @Property({ columnType: "boolean", default: false })
   is_automatic: boolean = false