Include consensus_hash in /new_burn_block and /new_block

[hstove]

I think it would be helpful to add consensus_hash to both the /new_burn_block and /new_block event dispatcher payloads.

The reason for this is somewhat selfish - when building slot watch, I try and correlate block proposals to burn blocks. But block proposals only have consensus_hash (and burn height), and I'm trying to only use event observer data, so I don't have a great way of mapping a proposal to a burn block.

If we add consensus_hash to these payloads, it'll make it really easy to correlate proposals to burn blocks without needing to rely on RPC requests.

This might also be helpful for the signer - it could "eagerly" update the burn tip's consensus hash without needing to make an RPC request.