Add conversion to properly parse query parameter propagationPolicy

[roycaihw]

What this PR does / why we need it:
This delete request query parameter has been broken for a year. I'm not sure if we want to deprecate the non-standard DeleteOptions body on delete request eventually.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #43329

Special notes for your reviewer:

Release note:

API server properly parses propagationPolicy as a query parameter sent with a delete request

/sig api-machinery

[liggitt]

can you add a test for this?

[roycaihw]

@liggitt do we want a unit test for the conversion function, or do we have some place to test the behavior of api server delete handler?

[roycaihw]

unit test for the conversion function added

[ncdc]

Don't you need to check if *input is nil first?

[roycaihw]

We don't check if *input and *output are nil in conversion functions, e.g. https://github.com/kubernetes/kubernetes/blob/7e75a09db6dc13218b4f5e06493115ae96f83774/staging/src/k8s.io/apimachinery/pkg/runtime/conversion.go
https://github.com/kubernetes/kubernetes/blob/7e75a09db6dc13218b4f5e06493115ae96f83774/staging/src/k8s.io/apimachinery/pkg/apis/meta/v1beta1/conversion.go
I will take another look to see where is it enforced.

[roycaihw]

It's enforced by

kubernetes/staging/src/k8s.io/apimachinery/pkg/conversion/converter.go

Line 497 in bed4531

func (c *Converter) doConversion(src, dest interface{}, flags FieldMatchingFlags, meta *Meta, f conversionFunc) error {

through

kubernetes/staging/src/k8s.io/apimachinery/pkg/conversion/helper.go

Lines 27 to 39 in bed4531

	func EnforcePtr(obj interface{}) (reflect.Value, error) {
	v := reflect.ValueOf(obj)
	if v.Kind() != reflect.Ptr {
	if v.Kind() == reflect.Invalid {
	return reflect.Value{}, fmt.Errorf("expected pointer, but got invalid kind")
	}
	return reflect.Value{}, fmt.Errorf("expected pointer, but got %v type", v.Type())
	}
	if v.IsNil() {
	return reflect.Value{}, fmt.Errorf("expected pointer, but got nil")
	}
	return v.Elem(), nil
	}

[ncdc]

Ok thanks 👍

[roycaihw]

@liggitt Would like another round of review :)

[liggitt]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt, roycaihw

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[k8s-ci-robot]

@roycaihw: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-kubemark-e2e-gce-big	294e00c	link	/test pull-kubernetes-kubemark-e2e-gce-big

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