make apps.json smaller via splitting it up based on server version

[tobiasKaminsky]

apps.json is too big.

We can split it by NC version, so that the server only needs to download their matching version.

[edward-ly]

For reference, we still have the /api/v1/platform/{platform-version}/apps.json endpoint documented here:
https://nextcloudappstore.readthedocs.io/en/latest/api/restapi.html#api-all-compatible-releases