Migrate to kyaml

[ultram4rine]

Closes #327.

Some notes:

• Seems like it possible to reduce some code, but current tests impose some restrictions. For example:

--- FAIL: TestKubeconfig_NamespaceOfContext_ctxNotFound (0.00s)
    namespace_test.go:34: expected err

Because without context we're expecting err, it hard to use Pipe(yaml.Lookup("contexts", "[name={ctxName}]", "context", "namespace")). If context doesn't exists, nil will be returned, just like if context doesn't have namespace, or kubeconfig doesn't have contexts.

• yaml.GetValue(node) is used instead of node.String() because last method doesn't work well with primitives like strings (e.g. "" instead of empty string).

[ahmetb]

This is excellent contribution, thanks. I learned this was possible after I implemented the initial Go version but never went back to incorporate, so thanks for doing the hard work there. I'll make sure to review soon.

[ultram4rine]

Issue from CI: https://github.com/kubernetes/client-go/issues/1269

Seems like client-go should be updated.

[ultram4rine]

Also maybe UpdateFile can be used.