### What
Creating a swap on an order with a discount leads to an incorrect difference due.
**Scenario**
- Create a store with minimum 2 products (Prod A, Prod B)
- Create a discount that only works for Prod A
- Create an order for Prod A with the discount applied
- Create a swap between Prod A and Prod B
**Expected outcome**
We would expect the difference_due amount to come out to the sum of:
- -1 * (price of prod a - discount applied to prod a)
- price of prod b
**Actual outcome**
Instead the discount is applied across both products when calculating difference due. This results in a total that is instead the sum of:
- -1 * (price of prod a - discount applied to prod a)
- price of prod b - discount on prod b ignoring the condition
### How
Adds `line_item.adjustments` to relations in cart retrieval prior to setting the difference_due to car total
Fixes CORE-361
* feat: swap details
* test: add get-swap and list-swaps route tests
* test: add swaps integration tests
* fix: use IdMap.getId in complete-cart unit test
commit 289d191 uses the IdMap.getId in the SwapServiceMock retrieve method, so a unit test in complete-cart needs to be adjusted accordingly
* fix: prefix default fields and totals with 'cart'
