Automatic merge from submit-queue
New command: "kubeadm token generate"
As part of #33930, this PR adds a new top-level command to kubeadm to just generate a token for use with the init/join commands. Otherwise, users are left to either figure out how to generate a token on their own, or let `kubeadm init` generate a token, capture and parse the output, and then use that token for `kubeadm join`.
At this point, I was hoping for feedback on the CLI experience, and then I can add tests. I spoke with @mikedanese and he didn't like the original propose of `kubeadm util generate-token`, so here are the runners up:
```
$ kubeadm generate-token # <--- current implementation
$ kubeadm generate token # in case kubeadm might generate other things in the future?
$ kubeadm init --generate-token # possibly as a subcommand of an existing one
```
Currently, the output is simply the token on one line without any padding/formatting:
```
$ kubeadm generate-token
1087fd.722b60cdd39b1a5f
```
CC: @kubernetes/sig-cluster-lifecycle
**Release note**:
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``` release-note
New kubeadm command: generate-token
```
afa99c68b8