Add ttrss-mailer-smtp plugin

.docker/app/Dockerfile

@@ -90,6 +90,6 @@ ENV TTRSS_DB_PORT="5432"
 
 ENV TTRSS_MYSQL_CHARSET="UTF8"
 ENV TTRSS_PHP_EXECUTABLE="/usr/bin/php83"
-ENV TTRSS_PLUGINS="auth_internal, note, nginx_xaccel"
+ENV TTRSS_PLUGINS="auth_internal, note, nginx_xaccel, mailer_smtp"
 
 CMD ${SCRIPT_ROOT}/startup.sh