chore: Update node version to 20 LTS

.changeset/clean-guests-guess.md

+---
+'@eth-optimism/chain-mon': patch
+---
+
+Bump node version to LTS node 20.9.0

.nvmrc

-v18.17.1
+v20.9.0

ops/docker/Dockerfile.packages

@@ -35,7 +35,7 @@ FROM us-docker.pkg.dev/oplabs-tools-artifacts/images/ci-builder:latest as foundr
 # we use it rather than alpine because it's not much
 # bigger and alpine is often missing packages for node applications
 # alpine is not officially supported by node.js
-FROM node:18.17.1-bullseye-slim as base
+FROM node:20.9.0-bullseye-slim as base
 
 # Base: install deps
 RUN apt-get update && apt-get install -y \