Add edit config dex in Go kubectl plugin

[TeddyAndrieux]

Component:

'salt', 'kubectl-plugin'

Why this is needed:

Centralized CLI

What should be done:

MetalK8s edit config dex command should be part of metalk8s Go kubectl plugin

kubectl metalk8s edit config dex
kubectl metalk8s edit config/dex

This command will open an editor to change the configuration for Dex.

Implementation proposal (strongly recommended):

This command will load the CSC of Dex display it in an editor to the user and then push the changes in Kubernetes and apply the changes using Salt.

It will be written in Go and should not use salt binaries at all, only interact directly with Salt API and should be able to run from outside of the cluster (check design documentation about Centralized CLI for more detail).

Follow kubectl best practice as much as possible.