fix: mixed patch formats

[gianlucam76]

sveltos-agent-config and sveltos-applier-config support both legacy bare patches and structured libsveltosv1beta1.Patch documents, but the two formats couldn't be mixed in one ConfigMap. The same override mechanism is used for per-cluster overrides via the
sveltosagent.projectsveltos.io/config-override-ref and sveltosapplier.projectsveltos.io/config-override-ref annotations.

getPatchesFromConfigMap parsed the whole ConfigMap as structured Patch documents. A single legacy-formatted entry caused that parse to fail for the entire ConfigMap. getSveltosAgentPatches then fell back to getSveltosAgentPatchesOld, which treated every entry, including already structured ones, as a raw legacy patch.

This PR fixes that by making the legacy/structured fallback happen per ConfigMap entry instead of per ConfigMap.

Fixes #496

[gianlucam76]

Tested locally with

apiVersion: v1
kind: ConfigMap
metadata:
  name: sveltos-agent-config
  namespace: projectsveltos
data:
  # Legacy bare-patch format: raw StrategicMerge patch, no "patch:" wrapper.
  # Adds label fv-legacy-patch=applied to the sveltos-agent-manager Deployment.
  legacy-patch: |-
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: sveltos-agent-manager
      labels:
        fv-legacy-patch: applied

  # Structured libsveltosv1beta1.Patch format: JSON6902 under "patch:", with
  # optional explicit "target:". Adds label fv-structured-patch=applied.
  structured-patch: |-
    patch: |-
      - op: add
        path: /metadata/labels/fv-structured-patch
        value: applied
    target:
      kind: Deployment
      group: apps
      name: sveltos-agent-manager

The sveltos-agent deployment

  apiVersion: apps/v1
  kind: Deployment
  metadata:
    annotations:
      deployment.kubernetes.io/revision: "1"
    creationTimestamp: "2026-08-08T15:45:48Z"
    generation: 1
    labels:
      control-plane: sveltos-agent
      fv-legacy-patch: applied
      fv-structured-patch: applied
    name: sveltos-agent-manager
    namespace: projectsveltos