Adding Power support for image gcr.io/cloud-builders/gcs-fetcher

Hi All,

We have a requirement for using the gcs-fetcher image on Power(ppc64le) architecture for knative deployment.

However, the images available here - https://console.cloud.google.com/gcr/images/cloud-builders/GLOBAL/gcs-fetcher?gcrImageListsize=30 have support for "amd64" only as seen below

docker image inspect gcr.io/cloud-builders/gcs-fetcher | grep Arch
"Architecture": "amd64",

I was able to build this image locally on a Power machine and validate it successfully and was looking for help in making the image @ gcr.io, multi-arch

Thank you!!