[Feature] Change to nginx-unprivileged image for better kubernetes support

[hsolberg]

Solves https://github.com/gchq/CyberChef/issues/1880

Not sure which image-repo you prefer to use, it's using Docker Hub in the pull-request (should be fine since its from a "Verified Publisher" and thus does not count towards the rate limit).

Alternative sources can be found here Amazon ECR - https://gallery.ecr.aws/nginx/nginx-unprivileged Docker Hub - https://hub.docker.com/r/nginxinc/nginx-unprivileged GitHub Container Registry - https://github.com/nginxinc/docker-nginx-unprivileged/pkgs/container/nginx-unprivileged Quay - https://quay.io/repository/nginx/nginx-unprivileged