chore(log): Log the time taken to process new blocks and transactions

[msbrogli]

We currently don't log how much it took to process new blocks and transactions received by the p2p network. This might be useful for debugging.

Acceptance Criteria

• Check the full node's log and find how long it took to process a new block or transaction.
• Export this metric to Prometheus.

Open questions

• What metrics should we export? Average? Sum? Maximum? Minimum?
• Should we use a sliding window for these metrics? If yes, how many blocks/transactions in the window?

[luislhl]

Should we also have a Prometheus metric measuring this?

[msbrogli]

Should we also have a Prometheus metric measuring this?

@luislhl I think so! And maybe an alert if the average gets too high.