Add the extra.symfony.docker flag

Dockerfile

@@ -32,10 +32,11 @@ COPY ./docker/h2-proxy/default.conf /etc/nginx/conf.d/default.conf
 ### PHP
 FROM php:${PHP_VERSION}-fpm-alpine AS symfony_docker_php
 
-RUN apk add --no-cache --virtual .persistent-deps \
+RUN apk add --no-cache \
 		git \
 		icu-libs \
-		zlib
+		zlib \
+		jq
 
 ENV APCU_VERSION 5.1.12
 RUN set -eux \

docker/app/docker-entrypoint.sh

@@ -16,6 +16,10 @@ if [ "$1" = 'php-fpm' ] || [ "$1" = 'bin/console' ]; then
     # The first time volumes are mounted, the project needs to be recreated
     if [ ! -f composer.json ]; then
         composer create-project "symfony/skeleton $SYMFONY_VERSION" tmp --stability=$STABILITY --prefer-dist --no-progress --no-interaction
+        jq '.extra.symfony.docker=true' tmp/composer.json > tmp/composer.tmp.json
+        rm tmp/composer.json
+        mv tmp/composer.tmp.json tmp/composer.json
+
         cp -Rp tmp/. .
         rm -Rf tmp/
     elif [ "$APP_ENV" != 'prod' ]; then