Add better Docker development and prod support

.docker/release/Dockerfile

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+# Inspired by the original Rainloop dockerfile from youtous on GitLab
+FROM php:7.3-fpm-buster
+
+ARG FILES_ZIP
+LABEL org.label-schema.description="SnappyMail webmail client image using nginx, php-fpm based on Debian Buster"
+
+ENV UID=991 GID=991 UPLOAD_MAX_SIZE=50M LOG_TO_STDERR=true MEMORY_LIMIT=128M SECURE_COOKIES=true
+ENV fpm.pool.clear_env=false
+
+# Install dependencies such as nginx
+RUN mkdir -p /usr/share/man/man1/ /usr/share/man/man3/ /usr/share/man/man7/ && \
+    apt-get update -q --fix-missing && \
+    apt-get -y upgrade && \
+    apt-get install --no-install-recommends -y \
+        apt-transport-https gnupg openssl wget curl ca-certificates nginx supervisor sudo \
+        unzip libzip-dev libxml2-dev libldb-dev libldap2-dev \
+        sqlite3 libsqlite3-dev libsqlite3-0 libpq-dev postgresql-client mariadb-client logrotate \
+        zip mlocate libmcrypt-dev libpcre3-dev libicu-dev \
+        build-essential chrpath libssl-dev \
+        libxft-dev libfreetype6 libfreetype6-dev \
+        libpng-dev libjpeg62-turbo-dev \
+        libfontconfig1 libfontconfig1-dev \
+        && \
+    rm -rf /var/lib/apt/lists/*
+
+# Install PHP extensions
+RUN php -m && \
+    docker-php-ext-configure ldap --with-libdir=lib/x86_64-linux-gnu/ && \
+    docker-php-ext-configure intl && \
+    docker-php-ext-configure gd --with-freetype-dir=/usr/include --with-jpeg-dir=/usr/include/ && \
+    docker-php-ext-install ldap opcache pdo_mysql pdo_pgsql zip intl gd && \
+    php -m
+
+# Install snappymail
+WORKDIR /tmp
+COPY ${FILES_ZIP} .
+RUN mkdir /snappymail && \
+    unzip -q ${FILES_ZIP} -d /snappymail && \
+    find /snappymail -type d -exec chmod 755 {} \; && \
+    find /snappymail -type f -exec chmod 644 {} \; && \
+    rm -rf ${FILES_ZIP}
+
+# Install other content
+COPY files /
+RUN chmod +x /entrypoint.sh && chmod +x /logrotate-loop.sh
+VOLUME /snappymail/data
+EXPOSE 8888
+CMD ["/entrypoint.sh"]