Use label selectors and upgrade master Nodes first

[jimmykarily]

We should be targeting Nodes in a more "Kubernetes native" way, using label selectors. The Kairos node labeler will also make more sense now. We automatically label Kairos nodes. The label can be used to target only Kairos nodes for upgrades. For now this targeting is left to the user but we can make it automatic in the future is we so desire.

This PR also:

• Sorts nodes with masters first. This makes the canary upgrades, upgrade master first which means we avoid deadlock situations in which a worker node running the operator gets rebooted in to a non-compatible (usually older) kubernetes version. This results in the worker not connecting to the cluster, and the operator not starting again. Thus, the rest of the Nodes never get an Upgrade Job create, stopping the whole process. The workaround would be to kill the operator Pod and let it be schefuled on a Node that is still schedulable. But doing masters first, ensures that there will be a compatible master to connect to when the operator Node comes back up.
• Refactors the code that handles the NodeOp status. Now there is a method to update the "Phase" and a method to update the reboot status.

Part of: kairos-io/kairos#769

[jimmykarily]

I need to split this PR in at least 2. The description only describes the first commit.

[jimmykarily]

I need to split this PR in at least 2. The description only describes the first commit.

updated the description instead of splitting (because the PR was already approved)