Automate generation of the Sparkle update appcast feed

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Recipe Robot uses Sparkle to alert users that a new update is available. Right now, new releases must be added to this Sparkle feed manually.

It would be very time-saving to build some automation to do this. An example workflow is provided here: https://medium.com/@alex.pera/automating-xcode-sparkle-releases-with-github-actions-bd14f3ca92aa

Even if the entire Xcode release workflow cannot be automated (as Recipe Robot uses a custom dmg made with DropDMG, not a simple zip file), generation of the appcast should be a first goal.