Issue #3494122 Set default values to new configs.

Closes #3494122

src/ToolbarHandler.php

@@ -221,8 +221,8 @@ class ToolbarHandler {
    * @return string|null
    */
   public function getCurrentRelease(): ?string {
-    $version_identifier = $this->config->get('version_identifier');
-    $version_identifier_fallback = $this->config->get('version_identifier_fallback');
+    $version_identifier = $this->config->get('version_identifier') ?? 'environment_indicator_current_release';
+    $version_identifier_fallback = $this->config->get('version_identifier_fallback') ?? 'deployment_identifier';
 
     $release = $this->getVersionIdentifier($version_identifier);
     if ($release !== NULL) {