Add our extension name to the PAT request prompt

[Merlin2001]

This is so the user has a clue what kind of PAT is required and which extension sent the request. There's also an open issue for VS Code to automatically show this information (which would mean we could revert to the old prompt or use Please provide PAT for Azure DevOps access)

(I've been wondering for weeks myself what caused this prompt because I had restored my VS Code from an old installation and didn't have any idea what kind of PAT I was missing)