Add convertion webhook for v1alpha1 and v1beta1 objects

[MartinForReal]

Is your feature request related to a problem? Please describe. Add convertion webhook for v1alpha1 and v1beta1 objects

We need to define the default version of crd and implement convert webhook

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Additional context https://kubebuilder.io/multiversion-tutorial/conversion

[Fei-Guo]

Our experiment shows that as long as there are no field changes, apiserver does automatic version conversions. The storage version is always v1beta1.