governance: burning fees function.

[chenquanyu]

We have not yet added the function of burning fees. We can send part of fees to an empty address in the governance contract to burn and configure this burning ratio in the policy contract.

Originally posted by @chenquanyu in #7 (comment)

[roman-khimov]

Can we do that in T3? While simple, burning is an important part of the project economics to me.