Move assets to own Dockerfile

core/admin/assets/Dockerfile

@@ -0,0 +1,14 @@
+# syntax=docker/dockerfile-upstream:1.4.3
+
+FROM node:16-alpine3.16
+
+COPY content ./
+RUN set -euxo pipefail \
+ && npm config set update-notifier false \
+ && npm install --no-fund \
+ && sed -i 's/#007bff/#55a5d9/' node_modules/admin-lte/build/scss/_bootstrap-variables.scss \
+ && for l in ca da de:de-DE en:en-GB es:es-ES eu fr:fr-FR he hu is it:it-IT ja nb_NO:no-NB nl:nl-NL pl pt:pt-PT ru sv:sv-SE zh; do \
+      cp node_modules/datatables.net-plugins/i18n/${l#*:}.json assets/${l%:*}.json; \
+    done \
+ && node_modules/.bin/webpack-cli --color
+