Add DONUT+FRAXBP pool to Ethereum Gauge Controller

Summary:
DONUTs are community points for Reddit’s r/ethtrader community. Originally DONUTs were completely community-driven, but have since been endorsed and integrated by Reddit. Currently, most onchain liquidity for DONUTs exists on Uniswap, and is incentivized.

DONUTs have raised significantly in value over the past month due to speculation of CEX listings, including a Kraken tweet.

The purpose of this gauge is to help introduce the DONUT and EthTrader communities to Curve, and to offer an alternative incentive structure, should the DONUT DAO decide to pursue it.

References/Useful links:

• Website    https://donut-dashboard.com/#/

• Github Page   https://github.com/orgs/EthTrader/repositories 

• Communities   https://reddit.com/r/ethtrader