Automatic merge from submit-queue (batch tested with PRs 56217, 56268, 56263, 56328, 56200). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Add docker-logins config to kubernetes-worker charm
**What this PR does / why we need it**:
This adds a `docker-logins` config option to the kubernetes-worker charm, which allows cluster operators to authenticate against docker registries so kubelet can pull containers from them.
**Release note**:
```release-note
Added docker-logins config to kubernetes-worker charm
```
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