sergii-ssh

Results 2 issues of sergii-ssh

Create SBOM even if the docker output set to context just skip scanning tars. Add `BillOfMaterialsURI` property to overwrite default location for SBOM

size/M

Currently secrets are managed manually for private prow cluster. We probably should move to terraform similar to istio-prow-build - `infra/gcp/istio-prow-build/secrets.tf`.