chore(core-flows,inventory,types,medusa): add fixes to inventory module + location levels api (#7629)

what:

- santizes inputs to prevent reserved_quantity from being updated directly
- inventory items create api can create location levels
- add validation to update quantity of reservation items
- general cleanup

RESOLVES CORE-2254

packages/medusa/src/api/admin/inventory-items/validators.ts

@@ -104,6 +104,7 @@ export const AdminCreateInventoryItem = z
     requires_shipping: z.boolean().optional(),
     thumbnail: z.string().optional(),
     metadata: z.record(z.string(), z.unknown()).optional(),
+    location_levels: z.array(AdminCreateInventoryLocationLevel).optional(),
   })
   .strict()