kubectl apply: fix --dry-run=client to output manifest values

[grandeit]

What type of PR is this?

/kind bug

What this PR does / why we need it:

When a resource already exists on the server, kubectl apply --dry-run=client was incorrectly outputting the current server state instead of the manifest values that would be applied.

The bug occurs because info.Get() replaces info.Object with the server response. For the normal apply path this is correct (we need server state for the 3-way merge), but for --dry-run=client the output should show what would be applied (the manifest), not what currently exists on the server.

This PR fixes the issue by saving the original manifest object before info.Get() and restoring it when --dry-run=client is used.

Which issue(s) this PR is related to:

Fixes #134640

Special notes for your reviewer:

The fix adds a test that verifies the output from kubectl apply --dry-run=client contains manifest values (port: 80) rather than server values (port: 9999).

Does this PR introduce a user-facing change?

Fixed a bug where `kubectl apply --dry-run=client` would output server state instead of manifest values when the resource already exists.

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

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: grandeit / name: Manuel Grandeit (8c99ba9)

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: grandeit
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