[6.x] Allow configurable emergency logger (#30873)

* Updated createEmergencyLogger

This allows for an emergency logger channel config item in config/logging.php

Use case: Serverless environment or Docker container without persistent storage. If main logger fails, logs may be lost. This will help prevent that by allowing us to specify stderr or stdout as the logger's path. (This will allow us to forward logs onto an ELK stack etc.)

* Update LogManager.php

* Not allowed to use the storage_path helper outside of Foundation

* Revert change to doc

src/Illuminate/Log/LogManager.php

@@ -163,9 +163,17 @@ protected function parseTap($tap)
      */
     protected function createEmergencyLogger()
     {
-        return new Logger(new Monolog('laravel', $this->prepareHandlers([new StreamHandler(
-                $this->app->storagePath().'/logs/laravel.log', $this->level(['level' => 'debug'])
-        )])), $this->app['events']);
+        $config = $this->configurationFor('emergency');
+
+        $handler = new StreamHandler(
+            $config['path'] ?? $this->app->storagePath().'/logs/laravel.log',
+            $this->level(['level' => 'debug'])
+        );
+
+        return new Logger(
+            new Monolog('laravel', $this->prepareHandlers([$handler])),
+            $this->app['events']
+        );
     }
 
     /**