Of course you can waive your right to appeal. It's a settlement. You waive lots of stuff in a plea, also your fourth amendment rights via allocution typically.
I agree that it's not necessarily unconscionable to allow this, but I'm curious about appeals on grounds of legal malpractice - if the lawyer who crafted your "no appeals" deal was on violation of their fiduciary duty, can you appeal the court's acceptance of the plea bargain?