feat(medusa): Attach or update cart sales channel (#1873)

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>

.changeset/lovely-news-attend.md

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+---
+"@medusajs/medusa": patch
+---
+
+Adds support for:
+- Attaching Sales Channel to cart as part of creation
+- Updating Sales Channel on a cart and removing inapplicable line items