fix: `cs_managed_kubernetes` - kubeconfig file create folders and use correct fs.FileMode

[hayorov]

if cs_managed_kubernetes .kubeconfig has value /foo/bar/.secret, ioutil.WriteFile failes with "No such file or directory"

Fixes:

• create intermediate folders (if required)
• Use correct fs.FileMode value

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[hayorov]

@xiaozhu36

[hayorov]

Hello, up!