chore: use sponge download api instead of hardcoded urls

[derklaro]

Motivation

Sponge provides a downloads api which allows to query the latest version of a sponge artifact. This is much nicer and removes the need to manually ensure that the download url of the sponge versions are always up-to-date.

Modification

Remove hardcoded sponge download urls from versions.json and replaced them with an install step which fetches the latest version from the sponge downloads api.

Result

Easy ensure that the downloaded version is always the latest one instead of relying on manual updates.