[Kairos Operator] - Handle upgrades

[mudler]

This card is to have a minimal Kairos operator, that currently could replace SUC for upgrading funcionalities.

TODO:

• Implement label filtering for Nodes - Use label selectors and upgrade master Nodes first kairos-operator#12
• Fix deadlock by upgrading masters first and documenting edge cases - Use label selectors and upgrade master Nodes first kairos-operator#12
• Remove duplication with field default values - Avoid default value duplication for boolean fields by using constants kairos-operator#11
• Update README to explain what it does, how it does it and how to install, debug etc. - Update the README kairos-operator#14
• Fix copyright text in files - Remove copyright text from various files and use LICENSE centrally kairos-operator#15
• Release