✨ Run validations before customizing a RPi image

[mauromorales]

Is your feature request related to a problem? Please describe.

When customizing a RPi image, if you made a mistake on your cloud config, you will only find out after building and copying to the SD card.

Describe the solution you'd like

Validations would run at the beginning of the process

Describe alternatives you've considered

n/a

Additional context

n/a

[jimmykarily]

We could add the validate command to the kairosctl so that the users can at least run it manually. Doing that automatically when people use the osbuilder flow would also be good.

[mudler]

That looks really tight to #958

[mauromorales]

I decided to add the command to kairosctl because I think it's going to be needed there anyway and updated the documentation. It's not solving #958 but I think that one will need a bit more thought