Add getter to return all supported log levels.

src/Monolog/Logger.php

@@ -329,6 +329,16 @@ class Logger implements LoggerInterface
       return $this->addRecord(static::EMERGENCY, $message, $context);
     }
 
+    /**
+     * Gets all supported logging levels.
+     *
+     * @return array
+     */
+    public static function getLevels()
+    {
+        return static::$levels;
+    }
+
     /**
      * Gets the name of the logging level.
      *