addOrUpdateToken method
Adds or updates a token definition.
If a token with the same key already exists, its definition is replaced.
Implementation
Future<void> addOrUpdateToken(TokenDef token) async {
final tokens = [
..._config.tokenDefs.where((item) => item.key != token.key),
token,
];
_config = _copyConfig(_config, tokenDefs: tokens);
await _storage.save(_config);
notifyListeners();
}