Add Recurse Option For Notebookutils.fs.ls

The current notebookutils.fs.ls() function will return the contents of a single directory. 

However, it is often the case that you need to recuse through child directories within a parent directory
Look at the Get-ChildItem cmdlet in PowerShell for a good example: Get-Child Item 

You can implement your own recursion, but I am willing to bet making multiple calls out to the synapse API is much less compute effective than just having the API be able to support recursive listing itself.

Please add a flag or parameter to get recursive results when using notebookutils.fs.ls()