Add install stats feedback to Packagist

[asgrim]

Since the PIE tool isn't Composer, it won't necessarily send feedback to Packagist about install stats.

This information is good to know about PIE usage in general, but also feedback for ext authors on how much folks are using their exts etc.

[asgrim]

For reference; stats are used to influence the order of things like https://packagist.org/search.json?q=<name>&type=<type> for example, you could have https://packagist.org/search.json?q=xdebug&type=php-ext-zend