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?

packages/types/src/workflow/index.ts

@@ -1,3 +1,4 @@
 export * as CartWorkflow from "./cart"
 export * as CommonWorkflow from "./common"
 export * as ProductWorkflow from "./product"
+export * as InventoryWorkflow from "./inventory"

packages/types/src/workflow/inventory/create-inventory-items.ts

@@ -0,0 +1,19 @@
+export interface CreateInventoryItemInputDTO {
+  sku?: string
+  hs_code?: string
+  weight?: number
+  length?: number
+  height?: number
+  width?: number
+  origin_country?: string
+  mid_code?: string
+  material?: string
+  title?: string
+  description?: string
+  thumbnail?: string
+  metadata?: Record<string, unknown>
+}
+
+export interface CreateInventoryItemsWorkflowInputDTO {
+  inventoryItems: CreateInventoryItemInputDTO[]
+}

packages/types/src/workflow/inventory/index.ts

@@ -0,0 +1 @@
+export * from "./create-inventory-items"