Support WPA2-PSK

It may be possible to do this through specifying a `key_mgmt` field like the Raspberry Pi `wifi_supplicant.conf` file.

`key_mgmt`: Specifies the key management protocol, which is typically WPA-PSK for WPA2 networks.

```
network={
ssid="YourNetworkSSID"
psk="YourNetworkPassword"
key_mgmt=WPA-PSK
}
```

We do need to check what encryption method is used for the `psk` field.

The issue names no files or tests. Start by locating the firmware's Wi-Fi configuration and WPA handling, then verify the required PSK encryption method against the Raspberry Pi example; done means WPA2-PSK networks can connect with the documented key_mgmt setting.

Written by the indexing model from the issue text.