Deterministic node token on installation to simplify cluster setup with scripts

[sourcehawk]

Currently, to set up a cluster one needs to install k3s on one first node and then extract the node token from the installation to be able to join other nodes on the cluster.

This makes scripting the cluster setup a hassle because the node token must be retrieved from one VM before k3s can be installed on other nodes. It would be great if the node token could be made deterministic before installation so that the node token does not need to be retrieved from the first installation in order to set up a cluster.

I am not aware of the reason for why the node tokens were implemented the way they are today, so if you see this as an impossible task, please let me know and I will close the issue.

[brandond]

Please check the conversation at #6175 (comment) - if you have any additional questions, follow up there. I'll be taking a pass at the documentation based on questions in that thread.