Move `config.dist.ts` to JSON

[KonradHoeffner]

Right now it is hard to configure after the build step, because the config files get rolled up along with all other JavaScript code into a single file.
This is relevant for example when we only check out the already build code on our web server.
Is it possible and does it make sense to configure Vite that it keeps the config files separate?

[KonradHoeffner]

According to https://vite.dev/guide/build.html#customizing-the-build this may be achieved using Rollup options via build.rollupOptions:

vite.config.js

export default defineConfig({
  build: {
    rollupOptions: {
      // https://rollupjs.org/configuration-options/
    },
  },
})

[KonradHoeffner]

Implemented in branch rollupconf, but I'm not sure if I should merge it into master as it is still difficult to configure in this form even if slightly better than before.
On the flip side, we make the build more complicated.
@Yagnap: What do you think?