add Prow configs for container image promoter
add Prow configs for container image promoter

These configs will run the container image promotion process, as
described in this KEP: https://github.com/kubernetes/enhancements/blob/master/keps/sig-release/k8s-image-promoter.md

These jobs only perform a promotion --- no garbage collection of images.
GC can be implemented in the future.

Prod jobs (periodic and postsubmit) run in the trusted cluster.

The dry run (presubmit) run in the regular cluster and do not mount any
secrets.

GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid