Nginx: Update the image and use the slim variant.

Removes some Nginx modules that I don't use (xslt, njs, geoip and image
filter).

nginx/Dockerfile

-FROM docker.io/nginx:1.25.3-alpine
+FROM docker.io/nginx:1.26.0-alpine-slim
 # hadolint ignore=DL3018
 RUN rm -rf /etc/nginx/conf.d/* && \
     chmod 777 /run && \