feat(consensus): Export state roots as a bounded hash range

[samcm]

This change adds two new metrics:

• eth_con_beacon_finality_checkpoint_hash following the head checkpoints for finalized/justified/previous_justified
• eth_con_beacon_head_slot_hash following the head slot

These metrics observe the state roots, and consistently convert them in to an integer between 0 and 65536. These metrics can then be used to observe which chain a beacon node is following by comparing this value at the current time to other nodes.

To work around scrape intervals, a query like this can be used to try and avoid noise:
max(eth_con_beacon_head_slot_hash)[1m].