Fix ArgoCD ServerSideDiff permanent OutOfSync diffs

Add explicit CRD/API defaults to manifests that were causing ArgoCD's
SSA dry-run to produce results different from live state:

- HTTPRoutes: add group, kind, weight defaults to parentRefs/backendRefs
- Kyverno ClusterPolicies: add skipBackgroundRequests, allowExistingViolations
- Tetragon TracingPolicies: add return, maxData, resolve, returnCopy defaults
- Gateway certificateRefs: add group="" default
- Guacamole Gateway: add group="" to certificateRefs

Add ignoreDifferences for resources that legitimately differ:
- Cilium cert Secrets (auto-generated, data always differs)
- Istio ValidatingWebhookConfiguration failurePolicy (istiod mutates)
- Crowdsec LAPI Secrets (randomly generated)
- ServiceMonitor/PodMonitor relabeling action defaults
- StatefulSet volumeClaimTemplates apiVersion/kind defaults

Persist argocd-cm ignoreDifferences config in ArgoCD Helm values.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infrastructure/kyverno/policies/require-drop-all-capabilities.yaml

@@ -15,6 +15,7 @@ spec:
   background: true
   rules:
     - name: require-drop-all
+      skipBackgroundRequests: true
       match:
         any:
           - resources:
@@ -55,6 +56,7 @@ spec:
                 - checkov
                 - external-secrets
       validate:
+        allowExistingViolations: true
         message: >-
           Containers must drop ALL capabilities (STIG V-242398).
           Add securityContext.capabilities.drop: ["ALL"] to each container.