Add Monolog channel to compiled log attributes

The channel is a relevant piece of metadata of a log entry.
This change includes the channel in the recorded attributes,
but remains backwards compatible and will not overwrite
existing extra or context fields named 'channel'.

Author: melkamar

src/Monolog/LogsHandler.php

@@ -144,6 +144,6 @@ public function __destruct()
      */
     protected function compileAttributes($record): array
     {
-        return array_merge($record['context'], $record['extra'], ['sentry.origin' => 'auto.log.monolog']);
+        return array_merge(['channel' => $record['channel']], $record['context'], $record['extra'], ['sentry.origin' => 'auto.log.monolog']);
     }
 }