What

This MR is a follow up of this one !16367 (merged). Here we are introducing the uptime metric for the evm_node

Manually testing the MR

1.Having an octez-evm-node build on this branch and running on the system using :

make octez-evm-node && octez-evm-node run observer --data-dir Testnet --network testnet --dont-track-rollup-node --init-from-snapshot

2.Then check the metrics :

watch "curl -s http://localhost:8545/metrics | grep performance | grep -v '#'"