Re-enable and Update ETH/USDT PERP Market

This proposal will re-activate the ETH/USDT PERP market with an updated initial margin ratio requirement to 19.5%. This new initial margin ratio will result in an effective initial max leverage of 5x which will help to ensure that liquidations are minimized. Since the vast majority of users never use more than 5x leverage, there should be no major hindrance on trading activities. In the future, a follow on proposal can be created to increase the leverage back to 10x and beyond.