Automatic merge from submit-queue
add rancher credential provider
This adds rancher as a credential provider in kubernetes.
@erictune This might be a good opportunity to discuss adding a provision for people to have their own credential providers that is similar to the new cloud provider changes (https://github.com/kubernetes/community/pull/128). WDYT?
```
release-note
Added Rancher Credential Provider to use Rancher Registry credentials when running in a Rancher cluster
```
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