Support coreCommands extensions

[pPrecel]

Description

Changes proposed in this pull request:

• remove registry commands group
• support coreCommands in extension configmap
• enable image-import and config commands if registry configmap exists

Related issue(s)

• https://github.com/kyma-project/cli/issues/2228

[pPrecel]

To test this functionality add the following ConfigMap with the registry extension:

apiVersion: v1
kind: ConfigMap
metadata:
  labels:
    kyma-cli/extension: resource
  name: registry.extension.cli
data:
  rootCommand: |
    name: registry
    description: Set of commands for Kyma registry
    descriptionLong: Use this command manage resources related to Kyma registry

  coreCommands: |
    - actionID: registry_config
    - actionID: registry_image-import

Now spells like

• go run main.go alpha registry
• go run main.go alpha registry config
• go run main.go alpha registry image-import

can be used