This allow GCP cloud build to fresh and incrementally build updated
docker containers to test upstream crosvm in CrOS tree efficiently.
Currently this resides in an experimental GCP project while being WIP.
TEST=Both fresh and incremental can build, emerge-hatch in pulled container
BUG=b:240692674
Change-Id: Id54014f347c00e4dae16674b430159dd8cfa67aa
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3934983
Commit-Queue: Zihan Chen <zihanchen@google.com>
Reviewed-by: Dennis Kempin <denniskempin@google.com>