phone number validation for new users

[edchapman88]

✅ Checklist

• I have searched open and closed issues for duplicates.
• This is a request for a new feature in the Data Safe Haven or an upgrade to an existing feature.
• The feature is still missing in the latest version.
• I have read through the documentation.
• This isn't an open-ended question (open a discussion if it is).

🍓 Suggested change

Add a lightweight (not too strict) phone number validation to the dsh users add command. To catch obvious user error early (e.g. number has too few or too many digits), before an Entra ID user is created.

🚂 How could this be done?

There is a PyPi package called phonenumbers that is a Python port of Google's libphonenumbers library. An error could be thrown by the dsh users add command is a phone number fails Google's validation.