Profiles: Specify default profile per-machine

## Summary

Profiles are great! I have a default profile which I use for all of my personal development and for school with Copilot, Rust extensions, etc., and a work profile which I use on my work machine with its own set of extensions and Copilot disabled due to corporate policy. However, every time I open up a new folder or file on my work machine, VS Code defaults to my personal profile, which is not only annoying but probably a violation of policy. I'd like to be able to change a setting so that my work machine uses my work profile by default instead of having to select it every time I open a new workspace.

## Current behavior

When opening a new workspace in VS Code, the current default profile is selected. This default is global to all machines logged in with settings sync enabled.

## Requested behavior

When opening a new workspace in VS Code, the current default profile is selected. This default is global to all machines logged in with settings sync enabled, with an optional override on a per-machine basis.