Support human readable timestamps in `custom-columns` printer

[ahmetb]

What would you like to be added:

Currently, --output=custom-columns=AGE:.metadata.creationTimestamp prints metav1.Time fields in ISO 8601 format (seen below), instead of the default "human readable" date strings like 3m or 16h that the default table printer uses.

kubectl get pods --output=custom-columns=NAME:.metadata.name,AGE:.metadata.creationTimestamp
NAME      AGE
foo-bar   2023-11-03T22:23:49Z

Why is this needed:

• It would be better for users of kubectl plugins in general. I think some users would still prefer the current behavior.
• Many kubectl plugins that are printing resourcecan importcli-runtimerepository and provide a default output format withcustom-columns` that uses creationTimestamp.

I'm not entirely sure if this is a valid ask, so please evaluate.

/sig cli

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