feat(config): Enhance config list/set output

[idsulik]

Description
Enhanced config list/set output.

• list: it's not obvious what happens when there is no config because the command returns empty output, now it shows a correct message.
  No config found for сurrent context "stage-nbg3"

• set: if you pass a wrong field name, it just says you passed a wrong field, but I think it'll be better to output what fields are valid:

  "test" is not a valid config field.
  Available fields are: debug-helpers-registry, update-check, survey, collect-metrics, update, kube-context, omitempty, 
  default-repo, local-cluster, kind-disable-load, k3d-disable-load, multi-level-repo, insecure-registries