UMIP 108 -Add GASETH-0921 as a supported price identifier

This UMIP will reference a synthetic token to be created with this price identifier. This token will be referred to as ‘uGAS’ and will represent the token that tracks this identifier with the most ETH volume on Sushiswap unless a different contract is determined by voters to be more legitimate.

This follows the exact same process as UMIP-22 but uses a different timestamp.

The DVM should support requests for a price that resolves to either the median monthly Ethereum gas price or a 2-hour Time-Weighted Average Price (TWAP) on the highest volume Sushiswap ETH/uGAS pool. The price resolution method to use will depend on the the timestamp the price request was made at.

For a price request made at or after the Unix timestamp 1633046400 (October 1, 2021 00:00:00 UTC), the price will be resolved with the median monthly gas price calculation defined for GASETH-1M-1M in UMIP-20 with the modification that it uses effective_gas_price instead of gas_price in order to account for EIP-1559. Full logic for this change is embedded in the Implementation section below.

For a price request made before 1633046400, the price will be resolved to a 2-hour TWAP for the Sushiswap price of the listed synthetic token in ETH. The synthetic token address will be listed in the Technical Specification section.