Packagist deprecated the original `packagist.org/p/username/package` endpoint in favor of v2 `packagist.org/p2/username/package` endpoint. Because of this, new packages aren't being found using v1.

This PR updates the Packagist service to use the new endpoint.

Some packages don't return the same data structure as others with the new api endpoints. This changes the validation schema to account for the potential differences.