Fix a bug where managedFields was not trimmed in scheduler

[likakuli]

What type of PR is this?

/kind bug
/kind regression

What this PR does / why we need it:

The PR #119556 was introduced to improve the memory usage of kube-scheduler by dropping the .metadata.managedFields field, which kube-scheduler does not require. However, after this commit c86f562, the pod informer's transform function is reset to the informerFactory's transform, which is nil. As a result, the previous optimization is no longer effective.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[likakuli]

kubernetes/staging/src/k8s.io/code-generator/cmd/informer-gen/generators/factory.go

Lines 127 to 134 in bdda0a5

	func WithCustomResyncConfig(resyncConfig map[{{.object|raw}}]{{.timeDuration|raw}}) SharedInformerOption {
	return func(factory *sharedInformerFactory) *sharedInformerFactory {
	for k, v := range resyncConfig {
	factory.customResync[reflect.TypeOf(k)] = v
	}
	return factory
	}
	}

kubernetes/staging/src/k8s.io/code-generator/cmd/informer-gen/generators/factory.go

Lines 152 to 158 in bdda0a5

	// WithTransform sets a transform on all informers.
	func WithTransform(transform {{.cacheTransformFunc|raw}}) SharedInformerOption {
	return func(factory *sharedInformerFactory) *sharedInformerFactory {
	factory.transform = transform
	return factory
	}
	}

The handling is different even though both are informer-level parameters. The current way of setting transform makes it very easy to write problematic code.