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.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"net/url"
+	"slices"
 	"time"
 
 	"github.com/pkg/errors"
@@ -184,10 +185,22 @@ func (e *defaultPodCommandExecutor) ExecutePodCommand(log logrus.FieldLogger, it
 }
 
 func ensureContainerExists(pod *corev1api.Pod, container string) error {
-	for _, c := range pod.Spec.Containers {
-		if c.Name == container {
-			return nil
-		}
+	existsAsMainContainer := slices.ContainsFunc(pod.Spec.Containers, func(c corev1api.Container) bool {
+		return c.Name == container
+	})
+
+	if existsAsMainContainer {
+		return nil
+	}
+
+	existsAsSidecar := slices.ContainsFunc(pod.Spec.InitContainers, func(c corev1api.Container) bool {
+		return c.RestartPolicy != nil &&
+			*c.RestartPolicy == corev1api.ContainerRestartPolicyAlways &&
+			c.Name == container
+	})
+
+	if existsAsSidecar {
+		return nil
 	}
 
 	return errors.Errorf("no such container: %q", container)