Automatic merge from submit-queue
[Federation] Make federation etcd PVC size configurable
This one implements one of the many TODO items pending in the previous set of kubefed PRs.
The design doc PR is at https://github.com/kubernetes/kubernetes/pull/34484
cc @kubernetes/sig-cluster-federation @madhusudancs
**Release note**:
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```
[Federation] kubefed init now has a new flag, --etcd-pv-capacity, which can be used to configure the persistent volume capacity for etcd.
```
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