docker: add git describe var to gateway image with front

Author: flomonster

docker/gateway-front.dockerfile

@@ -1,11 +1,20 @@
 FROM gateway_build
 
+RUN apk add npm && \
+    npm install -g @import-meta-env/cli && \
+    rm /etc/nginx/conf.d/default.conf
+
 # Copy the front
 WORKDIR /srv
 COPY --from=front_build /app/build /srv/front/
+COPY --from=front_build /app/.env.example /
 
 # Copy an example config file
 COPY --from=gateway_src ./gateway.prod.sample.toml /gateway.sample.toml
 COPY --chmod=755 ./gateway-entrypoint.sh /srv/entrypoint.sh
 ENTRYPOINT ["/srv/entrypoint.sh"]
-CMD ["/usr/local/bin/osrd_gateway"]
+
+ARG OSRD_GIT_DESCRIBE
+ENV OSRD_GIT_DESCRIBE=${OSRD_GIT_DESCRIBE}
+
+CMD ["sh", "-c", "npx import-meta-env -x /.env.example -p /srv/front/index.html && /usr/local/bin/osrd_gateway'"]