Add in-container nextcloud install

This increases the size of the container image, but reduces the reliance
on the external volume for loading application data. This couples the application
code to the container image rather than to the container state.

nginx/Dockerfile

@@ -1,4 +1,15 @@
-FROM docker.io/library/nginx:latest
+FROM docker.io/library/debian:latest AS unpack
+
+RUN apt-get update --yes
+RUN apt-get install unzip --yes
+RUN mkdir --parents /download
+
+WORKDIR /download
+
+ADD https://download.nextcloud.com/server/releases/latest.zip /download/latest.zip
+RUN unzip latest.zip
+
+FROM docker.io/library/nginx:latest AS final
 
 ENV NEXTCLOUD_DOMAIN=example.com
 ENV NEXTCLOUD_PHP_FPM_HOST=php-fpm-nextcloud:9000
@@ -7,4 +18,11 @@ ENV NEXTCLOUD_MAX_UPLOAD_SIZE=512M
 ADD nginx.conf.template /nginx.conf.template
 ADD docker-entrypoint.sh /docker-entrypoint.sh
 
+RUN mkdir --parents /var/www/html
+WORKDIR /var/www/html
+
+COPY --from=unpack /download/nextcloud /var/www/html/nextcloud
+RUN chown -R root:root nextcloud/
+RUN chmod -R 0755 nextcloud/
+
 ENTRYPOINT ["sh", "-c", "/docker-entrypoint.sh"]