(bug) Fix HelmReleaseSummary.FailureMessage never persisted

[gianlucam76]

When a Helm chart deployment fails, setHelmFailureMessageOnHelmChartSummary correctly sets FailureMessage on clusterSummary.Status.HelmReleaseSummaries[i] in memory, but this value was never written back to the API server.

The root cause is a sequencing issue: updateStatusForReferencedHelmReleases (which persists HelmReleaseSummaries) runs before walkChartsAndDeploy. After walkChartsAndDeploy fails and sets the FailureMessage in memory, updateStatusForNonReferencedHelmReleases then re-fetches a fresh ClusterSummary from the API and overwrites the status, so discarding the in-memory change entirely.

As a result, HelmReleaseSummaries[].FailureMessage always remained empty even after repeated failures, while featureSummaries[].failureMessage (set through a separate path) correctly reflected the error.

A secondary bug: setHelmFailureMessageOnHelmChartSummary was passed currentChart (the raw, pre-template spec) instead of instantiatedChart. The lookup compares ReleaseName/ReleaseNamespace against values stored in HelmReleaseSummaries, which are the instantiated values. When those fields contain Go templates, the lookup would silently find no match and the FailureMessage would not be set at all.

Fix consist in:

1. Pass instantiatedChart (post-template) instead of currentChart to setHelmFailureMessageOnHelmChartSummary so the lookup always matches what is stored in HelmReleaseSummaries.
2. In updateStatusForNonReferencedHelmReleases, before overwriting the status with the freshly fetched ClusterSummary, build an index of the in-memory FailureMessage values set by walkChartsAndDeploy and merge them into the entries being written. This ensures the failure from the current reconciliation round is persisted to the API.

Fixes #1692

[gianlucam76]

  status:
    dependencies: no dependencies
    featureSummaries:
    - consecutiveFailures: 1
      failureMessage: |
        chart: ingress-nginx, release: nginx, context deadline exceeded
      featureID: Helm
      hash: Ckr8tUz78ZCxNGIA/lR5QmvKVBZpFzuNCcjlUq/mE7k=
      lastAppliedTime: "2026-04-05T15:01:36Z"
      status: Failed
    helmReleaseSummaries:
    - failureMessage: context deadline exceeded
      releaseName: nginx
      releaseNamespace: nginx
      status: Managing
    - releaseName: postgres-operator
      releaseNamespace: postgres-operator
      status: Managing
      valuesHash: yj0WO6sFU4GCciYUBWjzvvfqrBh869doeOC2Pp5EI1Y=
    nextReconcileTime: "2026-04-05T15:01:46Z"

[gianlucam76]

Test added to functional verification