feat(customer): add customer group management apis (#6233)

**What**
```
POST /admin/customer-groups
POST /admin/customer-groups/:id
GET /admin/customer-groups/:id
DELETE /admin/customer-groups/:id
```

- Workflows

integration-tests/plugins/__tests__/customer/admin/list-customer-groups.spec.ts

@@ -1,63 +0,0 @@
-import { ModuleRegistrationName } from "@medusajs/modules-sdk"
-import { ICustomerModuleService } from "@medusajs/types"
-import path from "path"
-import { startBootstrapApp } from "../../../../environment-helpers/bootstrap-app"
-import { useApi } from "../../../../environment-helpers/use-api"
-import { getContainer } from "../../../../environment-helpers/use-container"
-import { initDb, useDb } from "../../../../environment-helpers/use-db"
-import adminSeeder from "../../../../helpers/admin-seeder"
-
-const env = { MEDUSA_FF_MEDUSA_V2: true }
-const adminHeaders = {
-  headers: { "x-medusa-access-token": "test_token" },
-}
-
-describe("GET /admin/customer-groups", () => {
-  let dbConnection
-  let appContainer
-  let shutdownServer
-  let customerModuleService: ICustomerModuleService
-
-  beforeAll(async () => {
-    const cwd = path.resolve(path.join(__dirname, "..", "..", ".."))
-    dbConnection = await initDb({ cwd, env } as any)
-    shutdownServer = await startBootstrapApp({ cwd, env })
-    appContainer = getContainer()
-    customerModuleService = appContainer.resolve(
-      ModuleRegistrationName.CUSTOMER
-    )
-  })
-
-  afterAll(async () => {
-    const db = useDb()
-    await db.shutdown()
-    await shutdownServer()
-  })
-
-  beforeEach(async () => {
-    await adminSeeder(dbConnection)
-  })
-
-  afterEach(async () => {
-    const db = useDb()
-    await db.teardown()
-  })
-
-  it("should get all customer groups and its count", async () => {
-    await customerModuleService.createCustomerGroup({
-      name: "Test",
-    })
-
-    const api = useApi() as any
-    const response = await api.get(`/admin/customer-groups`, adminHeaders)
-
-    expect(response.status).toEqual(200)
-    expect(response.data.count).toEqual(1)
-    expect(response.data.groups).toEqual([
-      expect.objectContaining({
-        id: expect.any(String),
-        name: "Test",
-      }),
-    ])
-  })
-})