The package overrides the default Laravel's VarDumpers and file context disappears

When this package is installed, it overrides VarDumper handler that comes from Laravel (`Illuminate\Foundation\Http\HtmlDumper` and `Illuminate\Foundation\Console\CliDumper`).

To compare, when the package is not installed:

And when it is installed, but the command not running:

The same in CLI.

When the command (`php artisan dump-server`) is not running, I would like to see the file context by default.

---

Suggestion:

As a suggestion, maybe the setting could be introduced to enable/disable the package? E.g. config:

```
...
'enabled' => env('DUMP_SERVER_ENABLED', true),
...
```

Then in `DumpServerServiceProvider` it could be conditionally loaded:
```
if ($this->app['config']->get('debug-server.enabled')) {
VarDumper::setHandler(function ($var) use ($connection) {
$this->app->makeWith(Dumper::class, ['connection' => $connection])->dump($var);
});
}
```

The command `php artisan dump-server` could give an error if it is not enabled:
```
if (! config('dump-server.enabled')) {
$this->error('The dump server is not enabled.');

return;
}
```

This would allow users to choose if they want it always enabled, or occasionally and would not override other VarDump registered handlers.

WDYT, I could open a pull request if it's reasonable idea.