New: Improve Manual Import logging when not parsing files

(cherry picked from commit 83f63590630ae0728fd9f9f03567a294934eebcc)

src/NzbDrone.Core/MediaFiles/TrackImport/Manual/ManualImportService.cs

@@ -170,6 +170,7 @@ private List<ManualImportItem> ProcessFolder(string folder, string downloadId, A
 
             if (artist == null && artistFiles.Count > 100)
             {
+                _logger.Warn("Unable to determine artist from folder name and found more than 100 files. Skipping parsing");
                 return ProcessDownloadDirectory(folder, artistFiles);
             }