Add gRPC server implementation and database integration for marketplace and products

internal/marketplace/repository.go

@@ -0,0 +1,8 @@
+package marketplace
+
+import "context"
+
+type Repository interface {
+	// GetMarketplaceByID retrieves a marketplace by its ID.
+	GetMarketplaceByID(ctx context.Context, id int) (*Marketplace, error)
+}