Non-async loading of featuredInstances.json5

[mblomdahl]

As discovered in #177, it is tricky to import a JSON5 file as you'd module-import a JSON (as we did before). I would like to return to having the featuredInstances.json5 imported as a module somehow. I've tried all the suggestions in the Using JSON5 with TypeScript documentation page, but everything failed. Instead, I would propose we have a pre-processing step (maybe a prepare script in the package.json?) that is responsible for always converting the featuredInstances.json5 → (type-validated) featuredInstances.json before starting/building/running the application. This would allow us to simply import featuredInstances from "../featured-instances.json" as before in the application.