Allow node latency data to be retrieved from Porter

[derekpierre]

From @KPrasch (nucypher/nucypher#3562 (review)):

Feature request (for this PR or a future PR): Publish current latency results in a JSON status endpoint or prometheus collector for continued optimization research and performance monitoring. 🤠

^ Think about retrieving node latency statistics from Porter. Given that Ursula currently doesn't collect latency stats (has no use for it at the moment), perhaps node latency data could be included as part of Porter prometheus data collection.