Make code about kubeconfig more generic

[pPrecel]

Description

Changes proposed in this pull request:

• create the kubeconfig flag and its usage in one place
• move flag creation to the cmdcommon pkg
• move kube.Client creation to the cmdcommon pkg

Related issue(s)

• https://github.com/kyma-project/cli/issues/2033#issue-2225406939

[pPrecel]

should be merged after this PR