Update website base image to node:20-alpine

[jahn18]

Description

• Resolves #334

Changing the base image to node-alpine. Alpine is better as it's faster and more lightweight compared to the official node images (which come with preset libraries).

Verification

• Tests all pass.
• Website functions fine.

Resources

• https://hub.docker.com/_/node
• https://stackoverflow.com/questions/53024267/docker-are-node-alpine-images-at-the-end-smaller-than-full-node-images