SyncFkResolver example

            'categories' => [
                ['id' => ['resolver' => 'dummy', 'value' => 'c1']],
                ['id' => ['resolver' => 'dummy', 'value' => 'c2']],
            ],

            // nesting case             'visibilities' => [
                ['visibility' => 1, 'salesChannelId' => ['resolver' => 'dummy', 'value' => 's1']],
            ],
        ];

        $resolver = new SyncFkResolver(
            new StaticDefinitionInstanceRegistry(
                [
                    ProductDefinition::class,
                    TaxDefinition::class,
                    ProductVisibilityDefinition::class,
                    SalesChannelDefinition::class,
                    CategoryDefinition::class,
                    ProductCategoryDefinition::class,
                ],
                $this->createMock(ValidatorInterface::class),
                $this->createMock(EntityWriteGatewayInterface::class)
            ),