data: format sample json files
Teach `data/fetch_from_gitlab.py` to save the JSON documents with human-readable formatting and in sorted order. Use `jq -S .` to format our existing data the same way. Formatted JSON documents are still sufficient to test our crate's deserialization of them and will make updates to new GitLab versions much more readable. While at it, also teach the script to remove the user identities, which we previously did by hand on each update.