Automatic merge from submit-queue (batch tested with PRs 41104, 41245, 40722, 41439, 41502)

Bump the minimum kubeadm control plane version to v1.6.0-alpha.2

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

There went in quite a lot of useful features into v1.6.0-alpha.2 that kubeadm will use.
This bump the minimum limit so we can depend on those features.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```
@mikedanese @errordeveloper @pires @dmmcquay @dgoodwin