[Request]: Get WiFi frequency info: 2.4 Ghz or 5 Ghz?

### Plugin

network_info_plus

### Use case

We're working on provisioning ESP devices, and it is crucial that these devices are only compatible with 2.4 GHz networks. We have to prevent the user from attempting to provision such devices on 5 GHz networks because it will fail.

Currently, I couldn't find any official way in Flutter to check if the device is connected to a 2.4 GHz or 5 GHz network.

### Proposal

This feature could be added to the `network_info_plus` package.

For example:
```dart
final frequency = await NetworkInfo().getWifiFrequency();

print('WiFi frequency: $frequency);
```