UMIP 160 -Add COVENANT_V1 price identifier

The COVENANT_V1 identifier is intended to be used with an Optimistic Distributor contract to verify Covenant bribing protocol payouts. Any address can propose distribution payouts of previously funded Covenant bribe through Merkle Distributor contract that follow previously posted bribe payout calculation methods and any address can dispute a proposal to UMA’s Optimistic Oracle within a challenge window.