Replace generate.py with a Next.js-native feature

[lucavallin]

Information about repositories is now fetched by the script generate.py. The script retrieves data from the GitHub API and then compiles it in data/generated.json and data/tags.json.

It should be possible to use https://nextjs.org/docs/basic-features/data-fetching/get-static-props to achieve this so that the process is perfectly integrated with Next.js. Also, we'd lose the dependency on Python and we wouldn't need those json files anymore. If this is not possible, it would still be nice to convert the generate.py script to Typescript to have only one language/ecosystem in the project.

When doing this, let's also convert repositories.toml to JSON so it can be handled natively by Typescript.

[lucavallin]

Done (almost)