feat: add UseServerSideApply to GeneratingPolicySpec

[remo-lab]

What this PR does

This PR adds a new optional field, spec.useServerSideApply, to GeneratingPolicy (and NamespacedGeneratingPolicy) specs.

This brings GeneratingPolicy in line with existing behavior in ClusterPolicy / Policy, where users can choose between:

• traditional Create/Update
• or Kubernetes Server-Side Apply (SSA)

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Why this is needed

Currently:

• useServerSideApply exists for generate rules in ClusterPolicy / Policy
• but GeneratingPolicy does not expose this option
• generated resources from GeneratingPolicy always use Create/Update

This is limiting for users running:

• multiple controllers managing the same resources
• environments that rely on SSA field ownership
• modern GitOps-style workflows

This gap is tracked in Issue [(https://github.com/kyverno/kyverno/issues/14853)].

---

What changed

• Added UseServerSideApply field to:

  • GeneratingPolicySpec
  • (and NamespacedGeneratingPolicy spec where applicable)

• Field is optional and defaults to false

• Includes comments and JSON tags consistent with existing API patterns

• CRDs regenerated accordingly

// UseServerSideApply controls whether to use server-side apply for generate rules.
// If set to true, generated resources will be created and updated using SSA.
// Defaults to false.
UseServerSideApply bool `json:"useServerSideApply,omitempty"`

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How this relates to the Kyverno implementation

This PR only defines the API contract.

A follow-up PR in the main kyverno/kyverno repository:

• reads this field from the policy spec

• passes it through the CEL engine and controllers

• switches resource creation/update logic between:

  • CreateResource / UpdateResource
  • and ApplyResource when SSA is enabled

Keeping the API change separate makes the review smaller and cleaner, and avoids mixing API evolution with controller logic.

---

Backward compatibility

• Fully backward compatible
• Existing GeneratingPolicies continue to behave exactly the same
• SSA is opt-in only

---

Related issue

• Fixes / implements: #14853

[remo-lab]

Hey @eddycharly ,
This PR adds the API field needed for useServerSideApply support in GeneratingPolicy.
A follow-up PR in kyverno/kyverno wires this through the engine and controllers to actually enable SSA for generated resources.
Would really appreciate a quick review when you get a chance — thanks!