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>.

Rename `MasterConfiguration` to `InitConfiguration` in the kubeadm v1alpha3 Config API

**What this PR does / why we need it**:
In v1alpha3, we have made the design decision that `MasterConfiguration` will be renamed `InitConfiguration`. This PR implements that change.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
ref: kubernetes/kubeadm#911
Depends on:
 - [x] https://github.com/kubernetes/kubernetes/pull/65776
 - [x] https://github.com/kubernetes/kubernetes/pull/65628
 - [x] https://github.com/kubernetes/kubernetes/pull/65629
 - [x] https://github.com/kubernetes/kubernetes/pull/65631
 - [x] https://github.com/kubernetes/kubernetes/pull/65940
 - [x] https://github.com/kubernetes/kubernetes/pull/65787

**Special notes for your reviewer**:
Most of the code is autogenerated, using just find and replace.
Please only review commits:
 - `Automated rename from MasterConfiguration to InitConfiguration`
 - `Rename MasterConfiguration to InitConfiguration in v1alpha3, but support both names for this release of kubeadm`

**Release note**:

```release-note
[action required] The `MasterConfiguration` kind in the kubeadm v1alpha2 API has been renamed `InitConfiguration` in v1alpha3
```
@kubernetes/sig-cluster-lifecycle-pr-reviews