DiagnoseMe: Migrate all gsutil usage to gcloud storage

Replaced all deprecated gsutil cp commands with modern gcloud storage cp
across build scripts, cloudbuild workflows, and Dockerfiles.

BUG=b:521782414
TEST=Built diagnosme contatiners and iso locally, also CQ passes

Change-Id: Ibd14bfd1fcfa20d257e5f4f14002ffab92a57bee
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/hwtools/diagnoseme/+/7913382
Reviewed-by: 488603086791@cloudbuild.gserviceaccount.com <488603086791@cloudbuild.gserviceaccount.com>
Tested-by: Łukasz Hajec <hajec@google.com>
Commit-Queue: Michał Headcrab Barnaś <barnas@google.com>
Reviewed-by: Michał Headcrab Barnaś <barnas@google.com>