Add returns processing logic to MSI

Description (*)

If a credit memo is created then MSI seems to do the following.

If an order is not shipped then it just cancels the reservation
If an order is shipped then it used the shipped from sources in the order (can be more than 1) and finds the one with the highest priority.
Also all sources accept returns, which is not the case in real life

Expected behavior (*)

The user should be able to select to which source the stock is sent. A dropdown is be presented under credit memo where the sources exist that "Accept returns"
Sources have an attribute flag "Accept returns" YES/NO hat defaults to YES
A new stock config setting is created where the admin can select the DEFAULT pre-selected source when a credit memo is issued.
Sources should exist that are not salable() but do Accept Returns (so a product is not sold during reconditioning)
OPTIONAL It would be good to also see in the credit memo credit some form of information from which source the product was shipped from originally. (This helps returns processing)

Benefits

Returns are a fact of life, often in fashion 20-30% or more. The admin should be able to select to which source the returns stock goes to. In addition many merchants have some kind of "incoming returns" or "reconditioning" source where all products go to: it would be great if this source is preselected. In addition the source where the product was shipped from should also be shown - only as information - for easier processing. The process below is a default process.

Additional information

Often there is a distinction between returns processing for shipped versus unshipped orders. Additional information and complete working flows can be obtained by reviewing this extension from M1 and all its settings https://www.safemage.com/multi-warehouse-inventory.html. Below we will give a brief overview

sources need a settings "can accept returns" yes/no
when processing a return in the credit memo field a drop down should exist to select where the product will be returned to and show a list of all sources (or all sources that have the flag "can accept returns" yes)
if an order item has not been shipped then the originating source is preselected (it is important though that in the dropdown one can see what the originating source was, so that if changed one still knows where it came from). Unshipped orders almost ~100% cases are returned to te originatign source.
if an order item has been shipped then a preferred source is preselected (set via the config or some attribute on the warehouse level). Shipped orders to the customer almost ~70% cases are NOT returned to te originatign source but rather some returns processing source.

magento / inventory