Add MariaDB container; add PDO connection; add error middleware

.env.develop

@@ -1,7 +1,23 @@
 # .env.development: Environment variables for local development
 
-# Set composer cache directory
+# composer: Set cache directory
 COMPOSER_CACHE_DIR=./.composer
 
-# Disable Twig cache
+# MariaDB container
+MYSQL_RANDOM_ROOT_PASSWORD=yes
+MYSQL_DATABASE=mailusers
+MYSQL_USER=mailaccountadmin
+MYSQL_PASSWORD=mailaccountadmin
+
+# App settings
+APP_DEBUG=true
+
+# - Disable Twig cache
 TWIG_CACHE_DIR=
+TWIG_STRICT=true
+
+# - Database credentials
+DB_HOST=db
+DB_DATABASE=mailusers
+DB_USER=mailaccountadmin
+DB_PASSWORD=mailaccountadmin