Add yarn to images to prepare for upcoming PR

php_fpm/Dockerfile

@@ -1,6 +1,10 @@
 ARG PHP_VERSION=8.1
 FROM php:${PHP_VERSION}-fpm-bullseye
 
+RUN apt-get update && \
+    apt-get install --no-install-recommends -y yarnpkg && \
+    rm -rf /var/lib/apt/lists/*
+
 ADD https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
 RUN chmod +x /usr/local/bin/install-php-extensions && \
     install-php-extensions @composer gd pdo_mysql mysqli zip exif