Remove use of pipeline/v1alpha1

[piyush-garg]

This will remove use of pipeline/v1alpha1 pkg
as this has been deprecated earlier and removed in
future releases

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Release Notes

Remove use of pipeline/v1alpha1

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[priyawadhwa]

/lgtm

[wlynch]

cc @ywluogg re #522

[ywluogg]

Ah thanks for that! I'm closing the other #530