Add gRPC server implementation and database integration for marketplace and products

internal/marketplace/entities.go

@@ -0,0 +1,8 @@
+package marketplace
+
+type Marketplace struct {
+	ID              int    `json:"id"`
+	BaseMarketplace int    `json:"base_marketplace"`
+	AuthData        string `json:"auth_data"`
+	WarehouseID     string `json:"warehouse_id"`
+}