I found the solution and thought to share so that it can be beneficial for all -
I was assuming that setting up the correct .htaccess in my website would do the trick but I was wrong as these are coming from third part so caching enabling has to be done at those not on my site.
Since I was using Google app engine and the trick is just open the app.yaml file for your application and add the following line (default_expiration: "4d 5h") something like
application: myapp
version: 1
runtime: python27
api_version: 1
threadsafe: true
default_expiration: "4d 5h"
handlers: