Moving the miner fund from consensus to policy makes it possible to do the following without a flag day upgrade:
* Change fund address
* Change fund amount
* Add staking rewards
This iteration of the patch (initial feedback in D12806) implements the policy after ConnectBlock but before the UTXO updates are flushed because alternatives are higher risk:
* Before ConnectTip/ConnectBlock - Parking a block before checking consensus rules would prevent a node from banning peers sending invalid blocks.
* After ConnectTip - Rewinding the in-progress state changes is fragile and prone to complications while backporting.
After Wellington activates, the miner fund will no longer be enforced as a consensus rule. Blocks not including the miner fund will be parked and voted on by avalanche.
Depends on D13150