Kbuild jobs download optimization

[nuclearcat]

When kbuild start process it need to download tarball artifact, which contain snapshot of kernel source code at specific tree, branch, commit.
This means same cluster building 35 kernel kinds - it will download same tarball at least 35 times.
With average size of tarball 200MB this is 7GB of data transfer (Azure $0.087 per GB = $0.609 per build). Often we have around 40-50 builds per 24h, so this is around $30 per day.
At month this is $900. This is not acceptable, if this is not optimized.
If we slash this at least 30 times, we can save $870 per month.
Potentially it is not happening yet, because we are scheduling build to cluster in same region. But if we start to schedule to different regions, or GCP/AWS we will have this problem.