Ingest `signer_signature_hash` from `/new_block` payload

This field is required to identify a Stacks block when given a `signer_signature_hash` like when dealing with `/stackerdb_chunks` messages.


There are a couple other additional new fields that we should also consider:
https://github.com/stacks-network/stacks-core/blob/447bb1519865be75a402f51cbb2d97f0db97186c/testnet/stacks-node/src/event_dispatcher.rs#L664-L675