BERLIN — In an unpredictable political year across Europe, the German election on Sunday has been considered the boring final act. Angela Merkel, the Continent’s most powerful figure, is expected to win a fourth term as chancellor after a colorless campaign. Yet if many Germans seem satisfied enough with their leader, others are unhappy with the wishy-washy consensus of the main political parties. Troubled by her immigration policy and her long tenure, some Germans are turning toward smaller, more ideological parties.