fix: correct plugin settings registration name and add save button

The plugin settings were not showing because the registration name was
incorrect. Changed from 'polaris' to 'headlamp-polaris-plugin' (matching
package.json name) and added displaySaveButton=true parameter.

According to Headlamp plugin API:
registerPluginSettings(name, component, displaySaveButton)

The name must match the plugin name from package.json.

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via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

src/index.tsx

@@ -66,7 +66,7 @@ registerRoute({
 });
 
 // Register plugin settings
-registerPluginSettings('polaris', PolarisSettings);
+registerPluginSettings('headlamp-polaris-plugin', PolarisSettings, true);
 
 // Register details view section for supported controller types
 registerDetailsViewSection(({ resource }) => {