Adding hint to the logger's error messages (#16034)

Co-authored-by: Jirka Borovec <6035284+Borda@users.noreply.github.com>
Co-authored-by: Carlos Mocholí <carlossmocholi@gmail.com>
Fixes #15143

(cherry picked from commit 7ce3825)

src/pytorch_lightning/trainer/connectors/logger_connector/fx_validator.py

@@ -174,7 +174,10 @@ def check_logging(cls, fx_name: str) -> None:
             )
 
         if cls.functions[fx_name] is None:
-            raise MisconfigurationException(f"You can't `self.log()` inside `{fx_name}`.")
+            raise MisconfigurationException(
+                f"You can't `self.log()` inside `{fx_name}`. HINT: You can still log directly to the logger by using"
+                " `self.logger.experiment`."
+            )
 
     @classmethod
     def get_default_logging_levels(