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>

.changeset/fast-buckets-marry.md

@@ -0,0 +1,7 @@
+---
+"medusa-react": patch
+"@medusajs/medusa-js": patch
+"@medusajs/medusa": patch
+---
+
+Add create-inventory-item endpoint

.changeset/slow-beers-train.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/admin-ui": patch
+---
+
+fix(admin-ui): create/update/delete inventory items according to inventory items on the variant