Create CI for testing the NGINX config

[MattIPv4]

As a lesson learnt from https://github.com/nodejs/nodejs.org/issues/5149, it'd be nice to have CI setup in this repository that validates the NGINX config for nodejs.org. I'm not sure the best way to do this, but perhaps just spinning up docker-compose with a mocked file system behind it that contains some fake dist/website files, and then a small E2E test suite that checks valid responses and 404s are all working as expected (including the localisation fallback behaviour).