Allow granular scopes based on extension preference

[ronakj]

Azure devops added support for granular scopes https://devblogs.microsoft.com/devops/new-azure-devops-scopes-now-available-for-microsoft-identity-oauth-delegated-flow-apps/. Previously we only had one default scope which allows access to all APIs.

Most developers using codespaces don't need tokens beyond vso.code_write (Git pull, push) & vso.packaging (Packaging - read). Getting full access tokens also risk developers making unintentional changes.

We can default to using the existing full scope, but allow developers to add the needed scopes in their devcontainer configuration using the VSCode settings customization option.

[ronakj]

@markphip something your team might want to look into if they have the bandwidth. Otherwise I will work on it next Feb/March whenever we have FHL week.

[ronakj]

Blocked on microsoft/vscode#201679