addCommand method
Add command.
Implementation
void addCommand(NmCommandPurpose purpose, NmTelecomL10n l10n) {
final value = selected;
if (value == null || value.isSystem) return;
final base = _purposeKey(purpose);
final id = _uniqueId(base, value.commands.map((item) => item.id));
final operation = NmUssdDialogOperation('${id}_ussd', start: const NmUssdStart(''));
final next = NmOperatorCommand(id: id, purpose: purpose, name: purpose.label(l10n), operations: [operation]);
_update(value.copyWith(commands: [...value.commands, next]));
selectedCommandId = id;
}