[Buildbot][IOS] Fix for deploying via AltStore/SideStore

altstore.json

TL;DR Small fix in https://buildbot.libretro.com/stable/altstore.json would vastly improve ability for iOS users to install and update RetroArch by using AltStore/SideStore to sideload.

I couldn't figure out how to make a PR of this (since I couldn't find where 'altstore.json' would be mentioned in source or ci scripts, maybe was manually uploaded?), or most fitting thread/channel in forum/discord, so I'll just file this generic issue, and try to tag @warmenhoven , which seems most active contributer on the ios part lately.

I've been using SideStore (a fork of AltStore) which most importantly lets iOS users sideload apps with only their iPhone (after first setup, no need for computer ot cable, at all), and secondly allowing custom Appstores.

I was very happy to find out someone (Warmenhoven?) had placed an altstore.json on tthe buildbot server (as I've had to create and maintain my own), but Sidestore chokes when trying to load it.

The only missing part is that the app object in the 'apps' array needs its own 'downloadURL' key, basicly a duplicate of the 'downloadURL' key from the current version object in the app's 'versions' array.

I just tested this by proxying the json on my local server, running a simple filter on it ('.apps[0].downloadURL=.apps[0].versions[0].downloadURL') and it loaded perfectly in SideStore.

This should probably be implemented in the automatic build, (maybe even accomodating several versions, hey maybe even betas) but I could attach my fixed version for quick upload.

Start by locating how buildbot.libretro.com/stable/altstore.json is created or uploaded; the issue says it may be manual and does not identify a source file or test. Compare the attached altstore.json with the published file and verify SideStore can load the result. Done means the app entry includes the requested downloadURL while preserving AltStore compatibility.