Make API config better splitting

in **apiconfig.dart** file when put **baseurl** as a variable,
make a split like this :

class ApiConfig{
// we put api url because we need to add image without api urn
static const **_baseUrl** = "http://demo-api.mr-dev.tech/";

static const _apiUrl = **_baseUrl+ "api/"**;
static const users = _apiUrl + 'users';
}