feat(medusa, admin-ui, medusa-react, medusa-js): Allow toggling of manage inventory (#3435)

**What**
- Toggle manage inventory in the inventory management modal

**How**
- Create/update/remove inventory item based on if `manage_inventory` is set and if an inventory item already exists
- Move all stock location updates to when the modal is submitted
- Add create-inventory-item endpoint in the core

Fixes CORE-1196

Co-authored-by: Sebastian Rindom <7554214+srindom@users.noreply.github.com>

packages/medusa-react/src/hooks/admin/inventory-item/mutations.ts

@@ -4,6 +4,8 @@ import {
   AdminPostInventoryItemsInventoryItemReq,
   AdminPostInventoryItemsItemLocationLevelsLevelReq,
   AdminPostInventoryItemsItemLocationLevelsReq,
+  AdminPostInventoryItemsReq,
+  AdminPostInventoryItemsParams
 } from "@medusajs/medusa"
 import { Response } from "@medusajs/medusa-js"
 import {
@@ -17,6 +19,29 @@ import { adminInventoryItemsKeys } from "./queries"
 
 // inventory item
 
+// create inventory item
+export const useAdminCreateInventoryItem = (
+  options?: UseMutationOptions<
+    Response<AdminInventoryItemsRes>,
+    Error,
+    AdminPostInventoryItemsReq
+  >
+) => {
+  const { client } = useMedusa()
+  const queryClient = useQueryClient()
+
+  return useMutation(
+    (payload: AdminPostInventoryItemsReq, query?: AdminPostInventoryItemsParams) =>
+      client.admin.inventoryItems.create(payload, query),
+    buildOptions(
+      queryClient,
+      [adminInventoryItemsKeys.lists()],
+      options
+    )
+  )
+}
+
+
 // update inventory item
 export const useAdminUpdateInventoryItem = (
   inventoryItemId: string,