Set the asset manifest OS and change the name of the installers manifests.
Currently arcade defaults to using OS-Platform as the asset manifest file name.
Installer does a ton of building in docker containers, which ends up generating
many overlapping names. This is a symptom and also likely hiding some non-determinsm.
To fix, change the name of the blob asset manifest name to include a "-installers" suffix.
Then alter the property names around a bit so that AssetManifestOS is set
prior to publish.proj's publish target being run.
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