Adds more explanatory message when SecretsMasker is not configured (#…

…17101)

The secrets masker added in 2.1.0 introduced requirement that
at least one SecretsMasker needs to be configured per task.

However this introduced problems for several users who migrated
from Airflow 1.10 and had their custom logging configuration
done without first copying the base airflow configuration.

The message about missing SecretsMasker was pretty cryptic for the
users. This PR changes the message to be much more descriptive
and pointing the user to the right place in documentation
explaining how advanced logging configuration should be done.

(cherry picked from commit 3a2e162)

airflow/utils/log/secrets_masker.py

@@ -102,7 +102,12 @@ def _secrets_masker() -> "SecretsMasker":
     for flt in logging.getLogger('airflow.task').filters:
         if isinstance(flt, SecretsMasker):
             return flt
-    raise RuntimeError("No SecretsMasker found!")
+    raise RuntimeError(
+        "Logging Configuration Error! No SecretsMasker found! If you have custom logging, please make "
+        "sure you configure it taking airflow configuration as a base as explained at "
+        "https://airflow.apache.org/docs/apache-airflow/stable/logging-monitoring/logging-tasks.html"
+        "#advanced-configuration"
+    )
 
 
 class SecretsMasker(logging.Filter):