[9.x] Support closures as values for about command

[SamuelMwangiW]

What

The PR proposes to support closures as values for the about command e.g

AboutCommand::add('Settings', [
    'value' => fn() => SettingModel::first()->value,
    'App Balance' => fn() => BalanceService::fetch(),
    'Computed Metric' => fn() => 6 ÷ 2(2+1),
]);

Why

I can see how handy to delay computation of some metrics and not have to evaluate the same with every request.
Also since its intended that Packages would be able to add sections to about command output

Tests

I couldn't find tests from the inital PR to add to but can add if requested.

Thanks for the great work