Automatic merge from submit-queue (batch tested with PRs 41857, 41864, 40522, 41835, 41991)

kubeadm: Demote --self-hosted to master config file.

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

kubeadm init --self-hosted was meant to be a short lived hack to enable self-hosted deployments until we're ready to make them the default. Rather than shipping this in 1.6 (for the first time) we will move this to the config file as it is presently only an advanced feature, leaving us with more well supported ways to remove it in the future.

**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**:

CC @luxas @pires @errordeveloper @dmmcquay 

**Release note**:

```release-note
NONE
```