Update endpoint for an inventory item

[haardikdharma10]

As a Website admin I need to update an inventory item (this will include updating the quantity, and restock_level fields) So that the inventory is always up to date.

Details and Assumptions

• Each Inventory Item has a unique ID
• Request will be PUT on **/inventory/{inventoryitem_id}

• The query should return an inventory item with any updated fields.

  Acceptance Criteria

  Given the user is authenticated as an admin
  When admin query PUT /inventory/inventoryitem_id
  Then the inventory item with the given ID should be returned with the fields that were updated.