What
Allow to create a cart with a sales channel, otherwise the default one is attached.
Also allow to update the sales channel on an existing cart and in that case the line items that does not belongs to the new sales channel attached are removed
How
Updating existing end points and service method to integrate the new requirements
Tests
Add new integration tests
Fixes CORE-270
Fixes CORE-272
Co-authored-by: Oliver Windall Juhl <59018053+olivermrbl@users.noreply.github.com>