feat(settings): load wireguard individual fields as secret files (#1348)

- Private key from `/run/secrets/wireguard_private_key` (path configurable with `WIREGUARD_PRIVATE_KEY_SECRETFILE`)
- Preshared key from `/run/secrets/wireguard_preshared_key` (path configurable with `WIREGUARD_PRESHARED_KEY_SECRETFILE`)
- Addresses from `/run/secrets/wireguard_addresses` (path configurable with `WIREGUARD_ADDRESSES_SECRETFILE`)

internal/configuration/sources/secrets/vpn.go

@@ -12,5 +12,10 @@ func (s *Source) readVPN() (vpn settings.VPN, err error) {
 		return vpn, fmt.Errorf("reading OpenVPN settings: %w", err)
 	}
 
+	vpn.Wireguard, err = s.readWireguard()
+	if err != nil {
+		return vpn, fmt.Errorf("reading Wireguard settings: %w", err)
+	}
+
 	return vpn, nil
 }