[DIP-5] Yearn vault for $DUSD stablecoin liquidity

Currently, yearn liquidity is being migrated to v2 vaults. The withdrawal fee from the vaults is turned off and hence this is a good time to perform the migration of the underlying $DUSD liquidity which was proposed in the Q2 roadmap.

Yearn vault choices:

1. crvSAAVE: Curve pool composed of aSUSD and aDAI. This pool was proposed by the DefiDollar team earlier. Details. This pool currently has $CRV and $AAVE incentives.

2. 3CRV: The curve pool with the highest trading volume but a high reliance on centralized stablecoins.

3. yUSD (yCRV vault): The $DUSD protocol currently parks liquidity in the yUSD v1 vault. Choosing this option would mean a liquidity migration from v1 to v2 vault.