feat(medusa-js, medusa-react, medusa): Prepare API for admin implementations (#3110)

********What********
Add `joinSalesChannels util to stock locations

Add the following endpoints to medusa-react
- inventory items
    - mutations
        - update
        - delete
        - update location level
        - delete location level
        - create location level
    - queries
        - list inventory items
        - get inventory item
        - list location levels
- Stock locations
    - mutations
        - create stock location
        - update stock location
        - delete stock location
    - queries
        - list stock locations
        - get stock locatoin
- Variants
    - queries
        - get inventory
- Reservations
    - mutations
        - create reservation
        - update reservation
        - delete reservation
    - queries
        - list reservations
        - get reservation
- sales channels 
  - mutations
    - associate location with sc
    - remove location association

**Why**
- Update clients to reflect new api endpoints in the core with inventory modules

Co-authored-by: Philip Korsholm <88927411+pKorsholm@users.noreply.github.com>

packages/medusa-react/test/hooks/admin/variants/queries.test.ts

@@ -1,4 +1,4 @@
-import { useAdminVariants } from "../../../../src"
+import { useAdminVariants, useAdminVariantsInventory } from "../../../../src"
 import { renderHook } from "@testing-library/react-hooks"
 import { fixtures } from "../../../../mocks/data"
 import { createWrapper } from "../../../utils"
@@ -16,3 +16,29 @@ describe("useAdminVariants hook", () => {
     expect(result.current.variants).toEqual(variants)
   })
 })
+
+describe("useAdminVariants hook", () => {
+  test("returns a variant with saleschannel locations", async () => {
+    const variant = fixtures.get("product_variant")
+    const { result, waitFor } = renderHook(
+      () => useAdminVariantsInventory(variant.id),
+      {
+        wrapper: createWrapper(),
+      }
+    )
+
+    await waitFor(() => result.current.isSuccess)
+
+    expect(result.current.response.status).toEqual(200)
+    expect(result.current.variant).toEqual({
+      ...variant,
+      sales_channel_availability: [
+        {
+          channel_name: "default channel",
+          channel_id: "1",
+          available_quantity: 10,
+        },
+      ],
+    })
+  })
+})