Add support for `BitlyClient` DI binding

[klimov-paul]

Package service provider should be adjusted allowing DI binding for BitlyClient class.

E.g. if I use type restriction for BitlyClient in controller or other class constructor, it should be resolved by DI. For example:

class SomeController extends Controller
{
    public function someAction(BitlyClient $bitly)
    {
        return $bitly->getUrl(...);
    }
}