feat: S&P Testnet Metrics

[ludamad]

Having these represented in grafana dashboard

• [ ] Time mem-tx to block-tx time(block produced with tx) - time(tx arrived in mempool) "How much time does it take for a sequencer to collect tx from its mempool/p2p and execute them to produce a block?"
• [ ] Time proposed to attested time(attestations collected) - time(l1-block-proposed) to help indirectly answer "How much time does it take for a committee to re-execute, verify state root, sign proposal and send it back to proposer?"
• [ ] Time governance proposal to completion Perhaps we just have nodes report their count of how many governance proposals they see whenever one is proposed or denied?

[just-mitch]

To answer the TODO question, no I don't think it is.