fix: keep Node SSR config optional during rollout

internal/deploymentconfig/config.go

@@ -245,6 +245,13 @@ func validateExactDocumentKeys(document []byte) error {
 			return err
 		}
 	}
+	nodeSsrValue, found := root["nodeSsr"]
+	if !found {
+		return nil
+	}
+	if _, ok := nodeSsrValue.(map[string]any); !ok {
+		return errors.New("nodeSsr must be a table")
+	}
 	nodeSsr, err := exactTable(root, "", "nodeSsr")
 	if err != nil {
 		return err
@@ -362,6 +369,9 @@ func (c Config) Validate() error {
 	default:
 		return fmt.Errorf("backend.type must be %q or %q", BackendTypeNative, BackendTypeContainer)
 	}
+	if c.NodeSsr.Type == "" {
+		return nil
+	}
 	if c.NodeSsr.Type != BackendTypeContainer {
 		return fmt.Errorf("nodeSsr.type must be %q", BackendTypeContainer)
 	}