feat(medusa,utils): added campaign get endpoints (#6125)

what:

adds endpoints for the following:

- list endpoint (RESOLVES CORE-1682)
- retrieve endpoint (RESOLVES CORE-1683)

packages/promotion/integration-tests/__tests__/services/promotion-module/campaign.spec.ts

@@ -27,6 +27,71 @@ describe("Promotion Module Service: Campaigns", () => {
     await MikroOrmWrapper.clearDatabase()
   })
 
+  describe("listAndCountCampaigns", () => {
+    beforeEach(async () => {
+      await createCampaigns(repositoryManager)
+    })
+
+    it("should return all campaigns and its count", async () => {
+      const [campaigns, count] = await service.listAndCountCampaigns()
+
+      expect(count).toEqual(2)
+      expect(campaigns).toEqual([
+        {
+          id: "campaign-id-1",
+          name: "campaign 1",
+          description: "test description",
+          currency: "USD",
+          campaign_identifier: "test-1",
+          starts_at: expect.any(Date),
+          ends_at: expect.any(Date),
+          budget: expect.any(String),
+          created_at: expect.any(Date),
+          updated_at: expect.any(Date),
+          deleted_at: null,
+        },
+        {
+          id: "campaign-id-2",
+          name: "campaign 1",
+          description: "test description",
+          currency: "USD",
+          campaign_identifier: "test-2",
+          starts_at: expect.any(Date),
+          ends_at: expect.any(Date),
+          budget: expect.any(String),
+          created_at: expect.any(Date),
+          updated_at: expect.any(Date),
+          deleted_at: null,
+        },
+      ])
+    })
+
+    it("should return all campaigns based on config select and relations param", async () => {
+      const [campaigns, count] = await service.listAndCountCampaigns(
+        {
+          id: ["campaign-id-1"],
+        },
+        {
+          relations: ["budget"],
+          select: ["name", "budget.limit"],
+        }
+      )
+
+      expect(count).toEqual(1)
+      expect(campaigns).toEqual([
+        {
+          id: "campaign-id-1",
+          name: "campaign 1",
+          budget: {
+            id: expect.any(String),
+            campaign: expect.any(Object),
+            limit: 1000,
+          },
+        },
+      ])
+    })
+  })
+
   describe("createCampaigns", () => {
     it("should throw an error when required params are not passed", async () => {
       const error = await service