feat: Add duo workflow panel

Description

This change introduces a new GitLab Duo Workflow Panel in the VS Code extension. The developers are separating the Duo Workflow functionality into two distinct components: one that appears in the editor area (tabs) and another that displays in a dedicated panel in the sidebar.

The main changes include:

• Adding a new webview ID constant DUO_WORKFLOW_PANEL_WEBVIEW_ID
• Updating package configuration to register the new panel view
• Renaming the sidebar view ID from gitlab-duo-workflow to gitlab-duo-workflow-panel
• Adjusting the webview registration logic to properly handle both workflow views
• Updating tests to reflect these changes

This refactoring allows the Duo Workflow feature to be displayed in multiple contexts within VS Code while maintaining a consistent user experience.

Related Issues

gitlab-org/editor-extensions/gitlab-lsp#1010 (closed)

Video

Screen Recording 2025-04-25 at 4.10.21 PM.mov

How has this been tested?

1. Ensure Duo Workflow is correctly setup
2. Checkout the branch for the LSP change and run npm run duo:workflow in the project's terminal
3. Do not enable the FF
4. Run command: Show duo workflow. Duo workflow should appear in a tab
5. On the sidebar, no new icons for workflow!
6. Enable the feature flag: "gitlab.featureFlags.duoWorkflowPanel": true,
7. Run the command show duo workflow and notice it opens in the sidebar!
8. the app should render
9. the app is usable
10. You also have a new icon in the sidebar

Screenshots (if appropriate)

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