fix(e2e): use correct image name in kustomize overlay

The e2e kustomize overlay tried to match
docker.io/library/plugin-barman-cloud but the base kustomization at
kubernetes/kustomization.yaml already transforms the bare
plugin-barman-cloud image to the GHCR name. The overlay must match
the base's output (ghcr.io/cloudnative-pg/plugin-barman-cloud-testing)
to override it.

Broken since b7daaac (#89) changed the base kustomization's newName
from docker.io/library/plugin-barman-cloud to the GHCR image without
updating the e2e overlay.

Closes #840

Signed-off-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>

Author: mnencia

test/e2e/e2e_suite_test.go

@@ -59,7 +59,7 @@ var _ = SynchronizedBeforeSuite(func(ctx SpecContext) []byte {
 		Resources: []string{barmanCloudKustomizationPath},
 		Images: []kustomizeTypes.Image{
 			{
-				Name:    "plugin-barman-cloud",
+				Name:    "ghcr.io/cloudnative-pg/plugin-barman-cloud-testing",
 				NewName: "registry.barman-cloud-plugin:5000/plugin-barman-cloud",
 				NewTag:  "testing",
 			},