add dev environment

docker/dev-ssu/Dockerfile

@@ -0,0 +1,8 @@
+FROM serversideup/php:8.2-fpm-nginx
+ARG POSTGRES_VERSION=15
+RUN apt-get update && apt-get install -y php-pgsql openssh-client
+RUN apt-get -y autoremove \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* /usr/share/doc/*
+
+COPY --chmod=755 docker/dev-ssu/etc/s6-overlay/ /etc/s6-overlay/