Allow to override the banner with its existing env variable

src/Settings/SystemSettings/CustomizationSettings.php

@@ -49,6 +49,7 @@ class CustomizationSettings
     #[SettingsParameter(
         label: new TM("settings.system.customization.banner"),
         formType: RichTextEditorType::class, formOptions: ['mode' => 'markdown-full'],
+        envVar: "BANNER", envVarMode: EnvVarMode::OVERWRITE,
     )]
     public ?string $banner = null;
 
@@ -58,4 +59,4 @@ class CustomizationSettings
     )]
     #[ValidTheme]
     public string $theme = 'bootstrap';
-}
+}