feat(Dockerfile.frontpage): add --sub-url flag to ENTRYPOINT command

The --sub-url flag is added to the ENTRYPOINT command in the Dockerfile
to allow the application to be served from a subdirectory. This is
useful when the application is deployed behind a reverse proxy that
routes requests to different applications based on the URL path.

docker/Dockerfile.frontpage

@@ -39,4 +39,4 @@ WORKDIR /www
 COPY --from=installer /app/apps/dicty-frontpage/dist ./
 ENV PORT 3000
 EXPOSE 3000
-ENTRYPOINT ["/usr/local/bin/app", "run", "-f", "/www", "-p", "3000", "--sf", "/assets"]
+ENTRYPOINT ["/usr/local/bin/app", "run", "-f", "/www", "-p", "3000", "--sf", "/assets", "--sub-url", "/"]