Disable imageDigest support in ztunnel controller

Currently, we have some pending work with the ztunnel images that
are used as imageDigests. Because of this, when deploying Ambient
profile using the OSSM operator, the ztunnel pod fails to come up.
This PR temporarily disables this functionality until proper support
is implemented.

Alternatives:
1. Default Image: If no image details are provided in the ZTunnel CR,
   the operator will use the default image from the helm chart.
2. Explicitly specify image details: Following a recent fix in the
   ztunnel controller (PR#568), users can specify image details within
   the ztunnel CR itself in one of the following ways.
   2.1: ztunnel.spec.values.ztunnel.image
   2.2: ztunnel.spec.values.global.hub/tag

Fixes: istio-ecosystem#581
Signed-off-by: Sridhar Gaddam <[email protected]>

controllers/ztunnel/ztunnel_controller.go

@@ -138,7 +138,17 @@ func (r *Reconciler) installHelmChart(ctx context.Context, ztunnel *v1alpha1.ZTu
 	userValues := ztunnel.Spec.Values
 
 	// apply image digests from configuration, if not already set by user
-	userValues = applyImageDigests(ztunnel, userValues, config.Config)
+	// TODO: Revisit once we support ImageOverrides for ztunnel
+	// userValues = applyImageDigests(ztunnel, userValues, config.Config)
+
+	if userValues == nil {
+		userValues = &v1alpha1.ZTunnelValues{}
+	}
+
+	// set image digest unless any part of the image has been configured by the user
+	if userValues.ZTunnel == nil {
+		userValues.ZTunnel = &v1alpha1.ZTunnelConfig{}
+	}
 
 	// apply userValues on top of defaultValues from profiles
 	mergedHelmValues, err := istiovalues.ApplyProfilesAndPlatform(

controllers/ztunnel/ztunnel_controller_test.go

@@ -337,7 +337,7 @@ func TestDetermineReadyCondition(t *testing.T) {
 	}
 }
 
-func TestApplyImageDigests(t *testing.T) {
+func PTestApplyImageDigests(t *testing.T) {
 	testCases := []struct {
 		name         string
 		config       config.OperatorConfig