fix: Display unauthenticated duo quick menu

Description

This MR resolves #1531 (closed) by handling the case when a user not authenticated in a GitLab instance opens a quick suggestions menu by clicking on a Duo icon in the bottom toolbar. This MR adds a Duo unavailable quick item that directs user to the authentication flow.

Related Issues

Resolves #1531 (closed)

How has this been tested?

1. Open a file where Duo code suggestions are supported
2. Click on a bottom DuoChat icon and check that the Duo Chat and code suggestions are shown in the quick suggestions list
3. Sign out by executing GitLab: Remove Account from VSCode command
4. Click on the DuoChat icon again and check that the Duo unavailable suggestion item is present in the list
5. Click on Duo unavailable item and check that the sign in flow starts

Screenshots (if appropriate)

2024-10-24_10-19-45.mkv

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes