Iraqis were casting ballots on Monday in the first elections for provincial councils in a decade, with the ruling Shi’ite Muslim alliance likely to extend its grip on power amid a boycott by populist cleric Moqtada al-Sadr, its main political rival. The election sets the stage for parliamentary elections scheduled for 2025, which will determine the balance of power in a nation where groups with close ties to Iran have gained ground in politics and the economy in recent years.