By Dan Weil The Federal Reserve seems like the only avenue to subdue inflation. Bill Ackman, the legendary hedge fund executive, has a different idea. At the moment, the Federal Reserve appears to be the only game in town to subdue inflation. The Fed has raised interest rates by 3 percentage points since March to fight the 8.3% surge in consumer prices for the 12 months through August. But hedge-fund star Bill Ackman, chief executive of Pershing Square Capital Management, has another idea. “Why don’t we reduce the Federal Reserve’s need to raise rates by expanding immigration now?” he wrote on…