feat: move create inventory to @medusajs/workflows (#5301)

**Why**
- We have some workflow-like flows in @medusajs/medusa. These should be moved over to the workflows package.
- Inventory Items <> Variant currently assume a 1-1 mapping. There should be support for a many-to-many mapping.

**What**
- PR introduces a feature flag for supporting many-to-many mappings for inventory and variants.
- Deletes legacy transaction handler in @medusajs/medusa.
- Adjusts existing createInventoryItems handler to remove dependency on variant data.

**Unkowns**
~~1. Couldn't find an existing test for the CreateProduct workflow. It should be tested that this still works as expected.~~
2. Have removed transaction managers as we should move to handling consistency through orchestration tooling. Are we ready for that?

integration-tests/plugins/__tests__/inventory/inventory-items/ff-many-to-many.js

@@ -0,0 +1,96 @@
+const path = require("path")
+const { ProductVariantInventoryService } = require("@medusajs/medusa")
+
+const {
+  bootstrapApp,
+} = require("../../../../environment-helpers/bootstrap-app")
+const { initDb, useDb } = require("../../../../environment-helpers/use-db")
+const { setPort, useApi } = require("../../../../environment-helpers/use-api")
+
+const adminSeeder = require("../../../../helpers/admin-seeder")
+
+jest.setTimeout(30000)
+
+const {
+  simpleProductFactory,
+  simpleOrderFactory,
+} = require("../../../../factories")
+const adminHeaders = { headers: { "x-medusa-access-token": "test_token" } }
+
+describe("Inventory Items endpoints", () => {
+  let appContainer
+  let dbConnection
+  let express
+
+  let variantId
+  let inventoryItems
+  let locationId
+  let location2Id
+  let location3Id
+
+  beforeAll(async () => {
+    const cwd = path.resolve(path.join(__dirname, "..", "..", ".."))
+    dbConnection = await initDb({ cwd })
+
+    const { container, app, port } = await bootstrapApp({ cwd, verbose: true })
+    appContainer = container
+
+    // Set feature flag
+    const flagRouter = appContainer.resolve("featureFlagRouter")
+    flagRouter.setFlag("many_to_many_inventory", true)
+
+    setPort(port)
+    express = app.listen(port, (err) => {
+      process.send(port)
+    })
+  })
+
+  beforeEach(async () => {
+    await adminSeeder(dbConnection)
+  })
+
+  afterAll(async () => {
+    const flagRouter = appContainer.resolve("featureFlagRouter")
+    flagRouter.setFlag("many_to_many_inventory", false)
+
+    const db = useDb()
+    await db.shutdown()
+    express.close()
+  })
+
+  afterEach(async () => {
+    jest.clearAllMocks()
+    const db = useDb()
+    return await db.teardown()
+  })
+
+  describe("Inventory Items", () => {
+    it("should create inventory item without variant id", async () => {
+      const api = useApi()
+
+      await api.post(
+        `/admin/inventory-items`,
+        {
+          sku: "TABLE_LEG",
+          description: "Table Leg",
+        },
+        adminHeaders
+      )
+
+      /** @type {ProductVariantInventoryService} */
+      const productVariantInventoryService = appContainer.resolve(
+        "productVariantInventoryService"
+      )
+
+      const inventoryService = appContainer.resolve("inventoryService")
+      const inventoryItems = await inventoryService.list()
+
+      expect(inventoryItems.length).toEqual(1)
+
+      const variants = await productVariantInventoryService.listByItem([
+        inventoryItems[0].id,
+      ])
+      expect(variants.length).toEqual(0)
+    })
+  })
+})

integration-tests/plugins/__tests__/inventory/inventory-items/index.js

@@ -345,7 +345,7 @@ describe("Inventory Items endpoints", () => {
 
       const inventoryItemCreateRes = await api.post(
         `/admin/inventory-items`,
-        { variant_id: variantId },
+        { variant_id: variantId, sku: "attach_this_to_variant" },
         adminHeaders
       )