By Jonathan Spicer ISTANBUL (Reuters) – Since Russia’s invasion of Ukraine sparked a flurry of Western sanctions on Moscow, at least one oligarch and thousands of other Russians have arrived in Turkey, seen as a safe place to stay, invest and hold assets despite its NATO membership. Acting as a safe haven raises risks for Turkey’s government, banks and businesses that could face tough decisions and penalties if the United States and others ramp up pressure on Moscow with broader “secondary” sanctions. Here is what is at stake: WHY IS TURKEY ATTRACTIVE TO RUSSIANS? Turkey has said Russian Presi…