ynh_install_php : add possibility to install extra extensions

[SimonMellerin]

This helper only install php and php-fpm, but other extensions are often need (like mysql, zip, curl...)

It could be great to add a list of extensions to install as a second argument

[maniackcrudelis]

If your app needs extensions, those extensions should be dependencies of your own app. Use ynh_install_app_dependencies in your scripts to add those. This helper has as a purpose only to install php itself.