fix: #be work around flaky npm mirror

backend/Dockerfile

@@ -4,6 +4,11 @@ LABEL maintainer="Paolo Brasolin <paolo.brasolin@eurac.edu>"
 WORKDIR /app
 
 COPY package*.json ./
+
+# FIXME: apparently today GH is congestioned and we need to use a chinese mirror.
+RUN npm config set sharp_binary_host "https://npmmirror.com/mirrors/sharp"
+RUN npm config set sharp_libvips_binary_host "https://npmmirror.com/mirrors/sharp-libvips"
+
 RUN npm install
 
 COPY . .