models/credentials library

1. uddoktapay package
2. documentation
3. models/credentials.dart

uddoktapay package

1. Libraries
2. controllers/payment_controller
3. core/services/api_services
4. models/credentials
5. models/customer_model
6. models/request_response
7. uddoktapay
8. utils/config
9. utils/endpoints
10. views/payment_screen
11. widget/custom_snackbar