Adding GAN Specialization notebooks with their images and relative data.

[FarshidNooshi]

Is your feature request related to a problem? Please describe.
adding GAN Specialization notebooks with their images and relative data.

Describe the solution you'd like

• add Course 1 notebook
• add Course 2 notebook
• add Course 3 notebooks
• update readme
• add course 1 data and certificates
• add course 2 data and certificates
• add course 3 data and certificates

Describe alternatives you've considered
create another repository

Additional context
The main readme of the repository contains the Deeplearning.AI TensorFlow developer structure that I want.