Changed ProgressBar init's type annotation to accept None (#2541)

* Changed ProgressBar init's type annotation to accept None

* fixed code formatting

* fixed progress bar string formatting

Co-authored-by: vfdev <[email protected]>

Author: Davidportlouis

ignite/contrib/handlers/tqdm_logger.py

@@ -117,7 +117,9 @@ class ProgressBar(BaseLogger):
     def __init__(
         self,
         persist: bool = False,
-        bar_format: str = "{desc}[{n_fmt}/{total_fmt}] {percentage:3.0f}%|{bar}{postfix} [{elapsed}<{remaining}]",
+        bar_format: Union[
+            str, None
+        ] = "{desc}[{n_fmt}/{total_fmt}] {percentage:3.0f}%|{bar}{postfix} [{elapsed}<{remaining}]",
         **tqdm_kwargs: Any,
     ):