Update mssqlclient.py

[kiriknik]

Add functionality to upload files

[gabrielg5]

Hey @kiriknik, sorry coming so late to this one

Thanks for this PR!

This branch should be rebased with latest changes as we've modified this example to make it callable from ntlmrelayx as an interactive shell; so some classes have been moved to other files (now it is in impacket/examples/mssqlshell.py)

Despite that, I've been checking it and have a few comments:

• Some error handling should be added to the command. I run it here and faced these, for example: file not found, remote file exists, permission denied... ie
• It should be checked if xp_cmdshell is enabled. If not, we will need to fail and ask the user to do so (I wouldn't enable it automatically, just in case...)
• tqdm should be added in the requirements and setup.py files - or removed and show progress in a different way -
• Instead than windows and linux in this log line "[+] MD5 hashes match\n[*] In windows: {} in linux: {}".format(md5sum,md5sum_uploaded), I would say something like local / remote or even something more verbose Impacket Host / SQL Server host
• A super tiny detail, alignment of commands description in the help output 🤓; and also the description of the new upload one can be changed to something that explains what the command does besides specifying what's required in those parameters
  

Thank you!

[gabrielg5]

Implemented requested changes.

• Validating if xp_cmdshell is enabled - returning if not
• Parsing command parameters with shlex
• Uploading file and validating its there with xp_fileexist

Removed addition of tqdm dependency. It is a nice UX but rather more related to the examples than to the library itself.
Linking with #1810 to take into account when working on splitting examples from library