Merge pull request #46247 from marun/fed-override-etcd-default-image

Automatic merge from submit-queue (batch tested with PRs 46201, 45952, 45427, 46247, 46062)

[Federation][kubefed]: Add support for etcd image override

This PR adds support for overriding the default etcd image used by ``kubefed init`` by providing an argument to ``--etcd-image``.  This is primarily intended to allow consumers like openshift to provide a different default, but as a nice side-effect supports code-free validation of non-default etcd images. 

**Release note**:

```release-note
'kubefed init' now supports overriding the default etcd image name with the --etcd-image parameter.
```
cc: @kubernetes/sig-federation-pr-reviews

hack/verify-flags/known-flags.txt

@@ -207,6 +207,7 @@ etcd-cafile
 etcd-certfile
 etcd-config
 etcd-keyfile
+etcd-image
 etcd-metrics-scrape-uri
 etcd-metrics-scrape-uri
 etcd-mutation-timeout