Bind Referral Reward to 1% Payback

Proposed to adjust the referral reward amount:

1. Bind the referral reward amount to 1% payback from the staked amount. Referral reward amount in LDO to be calculated each payout week based on ETH/USD and LDO/USD 14 days (whole referral period) TWAP to be 1% payback;
2. Limit minimum referral amount to 5 LDO for 1 ETH staked.
3. Limit maximum referral amount to 20 LDO for 1 ETH staked. Updated reward amount to take effect at the next referral period after DAO voting.

Link to the forum discussion: https://research.lido.fi/t/bind-referral-reward-to-1-payback/1021

Motivation Currently, the referral reward amount is 15 LDO for 1 ETH which is 2.4% payback (based on 14 days TWAP of LDO and ETH, see calculations below). Initial payback was ~1% at the date of the referral program launch. The referral reward amount is the key parameter that needs to be adjusted. Linking referral reward to 1% payback will help to use the rewarding budget most effectively, make the calculation process clear and transparent, keeping the referral program profitable and reaching the goals.