**What**
- Add `transformQuery` to get endpoints for product, order and cart
- ensure that the default relations (when getting a singular entity) includes sales channels when enabled
- Add `EmptyQueryParams` class in common types to prevent query parameters while using `transformQuery`
- update product-, order- and cartFactory to include sales channels if provided
- remove `packages/medusa/src/controllers/products/admin-list-products.ts`
**Testing**
- expands sales channel for single order
- expands sales channels for orders with expand parameter
- returns single product with sales channel
- expands sales channels for products with expand parameter
- returns cart with sales channel for single cart
Fixes CORE-293
Co-authored-by: Sebastian Rindom <7554214+srindom@users.noreply.github.com>
Co-authored-by: Adrien de Peretti <25098370+adrien2p@users.noreply.github.com>
