build(docker): optimize image size and security

- add mysql client binaries for database operations
- reduce php extensions to production essentials
- bind mysql and phpmyadmin to localhost only
- replace php-fpm.conf with php.ini for upload limits

.dockerignore

@@ -1,3 +1,3 @@
 *
 !docker/entrypoint.sh
-!docker/php-fpm.conf
+!docker/php.ini