Dockerfile: Upgrade dependencies

Start using moving tags for easier maintenance and earlier upgrades.

This might not be as deterministic, but from experience, the risks of breaking changes with node and nginx are low.

Author: schnatterer

Dockerfile

@@ -1,6 +1,6 @@
 ARG ENV=prod
-FROM node:18.14.0-alpine3.17 as node
-FROM nginxinc/nginx-unprivileged:1.23.3-alpine-slim as nginx
+FROM node:20-alpine as node
+FROM nginxinc/nginx-unprivileged:1-alpine-slim as nginx
 
 FROM node as aggregator 
 RUN mkdir -p /tmp/reveal /dist/scripts