**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>
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