Inspired by Rabindranath Tagore’s 1892 short story, the Kabuliwala, photographers Moska Najib and Nazes Afroz spent three years capturing the lives of the Kabuliwalas of Kolkata. Chris Finnigan talks to Moska about how their new exhibition in London reveals how generations of Afghan migrants have preserved their Pashtun identities in their new homeland. How did Tagore’s story…