This script will update release metadata in the cloud, and copy the already-built package to the right location and name on cloud storage.
The release metadata will be located in gs://flutter_infra/releases/releases.json, and the published packages will end up in gs://flutter_infra/releases/<channel>/<platform>/flutter_<platform>_<version><archive suffix>, where <channel>, <platform>, <version>, and <archive suffix> are determined by the script.
At the moment, it only supports dev rolls, but (once we know how those will work) should easily support beta rolls as well.
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