Include Codewars usernames and progress

All trainees by the end of the first module have signed up to Codewars.

Ideally in the batch view, we would see people's Codewars usernames, as well as the number of kata they've completed, their kyu, and maybe even their progress against particular collections of kata.

Getting the data is a little fiddly.

We can fetch codewars usernames from their Step 1 submission issues. @AnnaFYZ has produced a report of these links in https://lookerstudio.google.com/u/0/reporting/a41b99b7-c184-492c-a5f1-20e95dbf13f1/page/9Q8fF

The issues are unstructured, but hopefully it isn't too fiddly to pull out people's Codewars usernames from them once we get the issue body from a GitHub API.

We should probably generate a Google Sheet containing the GitHub username - Codewars username mapping, and pull that in dynamically. Alternatively, we could decorate this data into the existing GitHub accounts spreadsheet.

From there, the Codewars API conveniently allows getting user details, and completed kata, without any auth: https://dev.codewars.com/#content-type