f9c3218aac
**What** - added `SalesChannel` entity - added `SalesChannel` repository - added `SalesChannel` relations to the order, cart and store entities - added a migrations file **How** - introduced entities and relations under a new feature flag "sales-channels" Fixes CORE-271 Co-authored-by: Philip Korsholm <88927411+pKorsholm@users.noreply.github.com>