Motion #10: Enable Khala->Ethereum bridge and set fee

This is a follow up motion of Motion #9. By setting the bridge transfer fee, the backward bridge will be finally activated.

The fee we set is 375 PHA, around $300 at the current rate, to cover the Ethereum transaction fee. The fee was calculated based on the following facts:

  1. The Phala team runs 3 relayers for redundancy
  2. The relayers are configured to set the gas price up to 120 Gwei
  3. With the gas price of 120 Gwei, each cross-chain transaction costs around $100.

The bridge fee is moved to the Treasury. The Phala team will just send out Treasury proposal to reimburse the relayer transaction fee.

In the future, we would upgrade the bridge to lower down the costs, and open it to allow permissionless participation.