x/build/cmd/buildlet: add the ability to upload a zipped tarballl directly to GCS #53654
Description
Much like #53403:
As part of #47521, we are shifting to a model where we try to avoid streaming files through the coordinator on to the buildlet. We should explore granting the buildlet the ability to upload files to GCS or website. If the buildlet can upload files then we would not need to stream them from the buildlet to the coordinator to retrieve them.
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