Add new @k8s-release-robot permissions on k/sig-release and k/kubernetes

[david-mcmahon]

A new @k8s-release-robot user has been added to the project in order to facilitate the transfer of Kubernetes software release functions from Googlers (creating releases only on a desktop) to both Googler and non-Googler Kubernetes project contributors creating releases via https://cloud.google.com/container-builder.

Basic doc on functionality can be found here in the kubernetes/release repo.

In order for @k8s-release-robot to prepare and deliver releases via GCB, it must have write access to kubernetes/sig-release in order to assign owners and write labels to the release tracking issue created during a release and it must have 'repo admin' rights on kubernetes/kubernetes in order to push branches, tags and source code artifacts (CHANGELOG*.md, swagger.json) during releases. Essentially membership in @Kubernetes/kubernetes-release-managers.

[calebamiles]

Sent a notice to the mailing list announcing the addition.

[calebamiles]

Invitation sent