Read-only API for retrieving data

[laymonage]

Per discussion in #198 (comment).

The same XmlRpcPlugin that we removed in #198 was also responsible for the JSON RPC (/jsonrpc endpoint). The endpoint seems useful for extracting data to gain insights, e.g.

• the "Who contributed to Django X.Y?" project by Katie from DjangoCon Europe 2022: https://github.com/glasnt/dceu2022-sprints-work
• demo by Tobias from this gist: https://gist.github.com/rixx/422392d2aa580b5d286e585418bf6915

Instead of restoring the old API, which relies on an old Trac plugin and does not give us full control over the output, we probably want to create our own API.

@bmispelon has started a draft PR at django/djangoproject.com#1656.

For now, I think it's OK to limit the scope of the API to be read-only. If we find use cases for a write API, we can file a separate issue.

[laymonage]

Oops, just realised the API will live on the djangoproject.com repo. Will create a new one there instead...