Implement support for multiple PHP versions

This commit provides docker images and scripts to support multiple
Debian and PHP releases via containers.

buster_php7/Dockerfile-base

@@ -0,0 +1,31 @@
+FROM debian:buster
+LABEL maintainer="jan@dittberner.info"
+VOLUME /srv
+
+RUN apt-get update \
+    && DEBIAN_FRONTEND=noninteractive \
+    apt-get install -y --no-install-recommends \
+    dumb-init \
+    libnss-ldap \
+    nullmailer \
+    php-curl \
+    php-fpm \
+    php-gd \
+    php-imagick \
+    php-imap \
+    php-json \
+    php-mail \
+    php-mail-mime \
+    php-mbstring \
+    php-net-smtp \
+    php-net-socket \
+    php7.2-opcache \
+    php-pspell \
+    php-sqlite3 \
+    psmisc \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/*.*
+
+ADD --chown=root:root nsswitch.conf libnss-ldap.conf /etc/
+
+RUN rm -f /etc/php/7.2/fpm/pool.d/www.conf