His team having won the 2006 final match, Sankara was so popular that he was elected as Burkina Faso’s Minister for Magic. After a few days he resigned the post, in favour of continuing with his Quidditch career (Pm).
Joshua is a biblical name meaning "god is salvation" (QuickBabyNames).
His surname may refer to Thomas Sankara (1949-1987), who was President of Burkina Faso from 1983-1987 and a "charismatic and iconic figure of revolution" (Wikipedia).
From the Web
Writing by J.K. Rowling on Pottermore:
Pottermore enhanced reading experience: Quidditch World Cup
Screenshots of the original Daily Prophet coverage of the 2014 Quidditch World Cup on Pottermore: Imgur archive
Harry Potter Wiki: Joshua Sankara