Fix: change default value for metrics layout to be compatible with modals

[czernika]

This PR fixes error when using metrics and modals are presents at the same time (not within modal)

I will not open issue, basically steps to reproduce

1. Install Orchid, go to users list, click on "edit email" modal - everything is OK
2. Add dummy metric layout

public function query(): iterable
{
  return [
     // ...
     'metrics' => 1,
  ];
}

public function layout(): iterable
{
 // ...
 Layout::metrics(['Metrics' => 'metrics']),
}

3. Click same button again - modal data was not loaded (we can see skeleton and 500 error in a console)

Proposed Changes

Default data for metrics currently is empty array so it is passes is_array() check within layouts/metric.blade.php (currently line 13) and expects value key to be present. This PR should fix it