fix local development setup

[marc-se]

Currently, developers are running into an issue with a "wrong" data.json import.

In manager.ts, we import json from "./data.json";, but this file has been removed in https://github.com/digitalegarage/digitalegarage/commit/b883f35ddec0bd6b4f36736950085bf63830d48f

So we need a workflow to add the latest data.json file to the app directory while working locally without holding duplicate files in our git repository.

side note: works in deployment, cause data.json is getting copied from the root into app directory, via COPY data.json app/data/.