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Fix bad column alignment when using custom columns from OpenAPI schema

Columns printed by `kubectl get` weren't aligned properly when they were coming from the OpenAPI schema. 

This was caused by `CustomColumnPrinter.PrintObj`, which was creating a new `tabwriter.Writer` instead of re-using the tabwriter received through the `out` method parameter (basically, a tabwriter was writing to another tabwriter). Because the PrintObj flushed the tabwriter after writing each individual line, the column widths would reset.

**What this PR does / why we need it**:
This PR fixes the bad column alignment.

**Which issue(s) this PR fixes** 
Fixes #56282 

**Special notes for your reviewer**:
I've aligned how `CustomColumnPrinter.PrintObj` handles tabwriter with how `HumanReadablePrinter.PrintObj` does it (see https://github.com/kubernetes/kubernetes/blob/master/pkg/printers/humanreadable.go#L299-L303)

**Release note**:
```release-note
Fixed column alignment when kubectl get is used with custom columns from OpenAPI schema
```