feat: support backup hooks on native sidecars (#9403)

* feat: support backup hooks on sidecars
Add support for configuring Kubernates native
Sidecars as target containrs for Backup Hooks
commands. This is purely a validation level
patch as the actual pods/exec API doesn't make
any distinction between standard and sidecar
containers.

Signed-off-by: Gabriele Fedi <gabriele.fedi@enterprisedb.com>

* test: extend unit tests

Signed-off-by: Gabriele Fedi <gabriele.fedi@enterprisedb.com>

* chore: changelog

Signed-off-by: Gabriele Fedi <gabriele.fedi@enterprisedb.com>

* style: fix linter issues

Signed-off-by: Gabriele Fedi <gabriele.fedi@enterprisedb.com>

---------

Signed-off-by: Gabriele Fedi <gabriele.fedi@enterprisedb.com>

pkg/podexec/pod_command_executor_test.go

@@ -35,6 +35,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/remotecommand"
+	"k8s.io/utils/ptr"
 
 	v1 "github.com/vmware-tanzu/velero/pkg/apis/velero/v1"
 	velerotest "github.com/vmware-tanzu/velero/pkg/test"
@@ -253,6 +254,15 @@ func TestEnsureContainerExists(t *testing.T) {
 					Name: "foo",
 				},
 			},
+			InitContainers: []corev1api.Container{
+				{
+					Name: "baz",
+				},
+				{
+					Name:          "qux",
+					RestartPolicy: ptr.To(corev1api.ContainerRestartPolicyAlways),
+				},
+			},
 		},
 	}
 
@@ -260,7 +270,13 @@ func TestEnsureContainerExists(t *testing.T) {
 	require.EqualError(t, err, `no such container: "bar"`)
 
 	err = ensureContainerExists(pod, "foo")
-	assert.NoError(t, err)
+	require.NoError(t, err)
+
+	err = ensureContainerExists(pod, "baz")
+	require.EqualError(t, err, `no such container: "baz"`)
+
+	err = ensureContainerExists(pod, "qux")
+	require.NoError(t, err)
 }
 
 func TestPodCompeted(t *testing.T) {