Ensure logger allows to use placeholders and take args from context

[samdark]

See https://peakd.com/hive-168588/@crell/using-psr-3-placeholders-properly

[terabytesoftw]

Our logger allows placeholders for messages, you just have to add it to the documentation.

https://github.com/yiisoft/log/blob/975566e4f8e41a56dbdd7e64d373720e161bff4b/tests/MessageTest.php#L55