GitLab export format

I’m having second thoughts about using the GItLab export format as a pivot. It is undocumented and moves relatively frequently. Reverse engineering it to write an import function using the API may be more work than writing a export function using the API and define a pivot format specific to fedeproxy.

Is a fedeproxy format, documented with a JSON-schema that is also used for validation using jschon was bootstrapped.