Automatic merge from submit-queue. 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>.
Enable scaling fluentd-gcp resources using ScalingPolicy.
See https://github.com/justinsb/scaler for more details about ScalingPolicy resource.
**What this PR does / why we need it**:
This is adding a way to override fluentd-gcp resources in a running cluster. The resources syncing for fluentd-gcp is decoupled from addon manager.
**Special notes for your reviewer**:
**Release note**:
```release-note
fluentd-gcp resources can be modified via a ScalingPolicy
```
cc @kawych @justinsb
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