Improve error message for invalid Helm chart repository URLs

Wrap the errors from CacheIndex() and LoadFromPath() in reconcileSource
with a helm-CLI-style message that includes the configured repository URL.
When the index cannot be fetched or fails to parse (e.g. server returns
HTML instead of YAML), the user now sees:

  looks like "https://example.com" is not a valid chart repository or
  cannot be reached: <underlying error>

instead of the cryptic YAML parse error or generic fetch failure.

Fixes #654

Signed-off-by: Ogulcan Aydogan <ogulcanaydogan@hotmail.com>

Author: ogulcanaydogan

internal/controller/helmrepository_controller.go

@@ -450,7 +450,7 @@ func (r *HelmRepositoryReconciler) reconcileSource(ctx context.Context, sp *patc
 	// Fetch the repository index from remote.
 	if err := newChartRepo.CacheIndex(); err != nil {
 		e := serror.NewGeneric(
-			fmt.Errorf("failed to fetch Helm repository index: %w", err),
+			invalidChartRepoError(obj.Spec.URL, err),
 			meta.FailedReason,
 		)
 		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, e.Reason, "%s", e)
@@ -476,7 +476,7 @@ func (r *HelmRepositoryReconciler) reconcileSource(ctx context.Context, sp *patc
 	// Load the cached repository index to ensure it passes validation.
 	if err := chartRepo.LoadFromPath(); err != nil {
 		e := serror.NewGeneric(
-			fmt.Errorf("failed to load Helm repository from index YAML: %w", err),
+			invalidChartRepoError(obj.Spec.URL, err),
 			sourcev1.IndexationFailedReason,
 		)
 		conditions.MarkTrue(obj, sourcev1.FetchFailedCondition, e.Reason, "%s", e)
@@ -723,3 +723,10 @@ func (r *HelmRepositoryReconciler) migrationToStatic(ctx context.Context, sp *pa
 
 	return ctrl.Result{}, nil
 }
+
+// invalidChartRepoError formats an error indicating the given URL is not
+// a valid Helm chart repository or cannot be reached, mirroring the
+// `helm repo add` CLI output.
+func invalidChartRepoError(repoURL string, err error) error {
+	return fmt.Errorf("looks like %q is not a valid chart repository or cannot be reached: %w", repoURL, err)
+}