Automatic merge from submit-queue

Add flag to set CNI bin dir, and use it on gci nodes

**What this PR does / why we need it**:

When using `kube-up` on GCE, following #31023 which moved the workers from debian to gci, CNI just isn't working.  The root cause is basically as discussed in #28563: one flag (`--network-plugin-dir`) means two different things, and the `configure-helper` script uses it for the wrong purpose.

This PR adds a new flag `--cni-bin-dir`, then uses it to configure CNI as desired.

As discussed at #28563, I have also added a flag `--cni-conf-dir` so users can be explicit 

**Which issue this PR fixes** : fixes #28563

**Special notes for your reviewer**:

I left the old flag largely alone for backwards-compatibility, with the exception that I stop setting the default when CNI is in use.  The value of `"/usr/libexec/kubernetes/kubelet-plugins/net/exec/"` is unlikely to be what is wanted there.

**Release note**:
```release-note
Added new kubelet flags `--cni-bin-dir` and `--cni-conf-dir` to specify where CNI files are located.
Fixed CNI configuration on GCI platform when using CNI.
```