[Feature] Add support for custom env reader functions

Right now the plugin works great with laravel using `env('SOMETHING')`.

However I like to create a second helper for when the app just won't run without an environment variable defined.

```php
function env_or_throw($key, $default = null)
{
return env(
$key,
$default ?? fn() => throw new \Exception("Missing require environment variable '{$key}'.")
);
}
```

It would be great if we could specify that `env_or_throw` or `my_special_env_function` was an `env` alias.