[PIP-041] Add Stader's ETHx as collateral to mint mkUSD

This proposal is to onboard an ETHx vault for minting mkUSD. The suggested vault parameters are conservative and commensurate with ETHx’s risk profile.

Suggested Parameters Mint Cap: 10m mkUSD MCR: 120% Mint Fee: 0% Borrow Interest Rate: 10%

Read more: https://gov.prismafinance.com/t/pip-041-add-staders-ethx-as-collateral-to-mint-mkusd/201