[FEATURE] Github action to publish iOS build to appetize

[jfmcquade]

What?
Follow-up to #2234.

We should be able to publish iOS builds to appetize, as we currently do for Android. This will likely first require a action to generate ios builds, see #2240.

Why?
This would be useful as soon as possible to allow non-Mac owners to perform functional testing on iOS related features.

Other details
We'll want to be able to publish iOS builds to appetize both from arbitrary content repos and from the main code repo (in the latter case, likely checking out the content from the debug repo). I'm not sure if the latter case is currently possible for Android builds or not.

An intial build, manually uploaded to appetize, is available here.