Prop 95: [SIPS-093] Update stETH Pricing in Price Router

This text proposal is to update stETH pricing in the price router. If the proposal is accepted, a Steward update will enable the strategists to enact the change. For more information, see the corresponding forum post: https://community.sommelier.finance/t/sips-093-upcoming-proposal-to-update-steth-pricing/1210