"datastore.upload_files" is deprecated after version 1.0.69

In `azureml-core 1.37.0.post1`, we have gotten the warning message like the below:
```
"datastore.upload_files" is deprecated after version 1.0.69. Please use "FileDatasetFactory.upload_directory" instead. See Dataset API change notice at https://aka.ms/dataset-deprecation.
```

It seems that the URL points to [this page](https://github.com/Azure/MachineLearningNotebooks/blob/b05ff80e9dfc3d1a38031e9e701ebed841760463/how-to-use-azureml/work-with-data/dataset-api-change-notice.md), but there is no information for migration.

`datastore.upload_files` could specify files as a list explicitly even if the directory contains the file we don't want to upload like credential data, the file which contains personal data before processing, and so on.

How to use `FileDatasetFactory.upload_directory` as same as `datastore.upload_files`?