Add docker test environment

Dockerfile

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+FROM php:8-cli
+
+RUN apt update \
+        && apt install -y \
+            libpng-dev \
+            libicu-dev \
+            libpq-dev \
+            libzip-dev \
+            zip \
+            zlib1g-dev \
+            locales \
+            locales-all \
+            libmagickwand-dev \
+            libwebp-dev \
+        && pecl install imagick \
+        && docker-php-ext-configure gd --with-freetype --with-jpeg --with-webp \
+        && docker-php-ext-enable imagick \
+        && docker-php-ext-install \
+            intl \
+            opcache \
+            pdo \
+            pdo_pgsql \
+            pdo_mysql \
+            pgsql \
+            fileinfo \
+            mysqli \
+            gd \
+            bcmath \
+            exif \
+            zip \
+        && apt-get clean
+
+# install composer
+#
+RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer

docker-compose.yml

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+version: '3'
+
+services: 
+  tests:
+    build: ./
+    working_dir: /project
+    command: bash -c "composer install && ./vendor/bin/phpunit -vvv"
+    volumes:
+      - ./:/project