Add StartTime and CompletionTime in job status

[Jeffwan]

This is not a breaking API change. I think it should be fine to add into v1alpha1.

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This change is 

[k8s-ci-robot]

Hi @Jeffwan. Thanks for your PR.

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[terrytangyuan]

@Jeffwan Tests need to be updated as well since additional fields are expected.

[Jeffwan]

@terrytangyuan Sure. I will add test.

[terrytangyuan]

/lgtm

[rongou]

/lgtm
/approve

[k8s-ci-robot]

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