feat: Add Open in GitLab to commits in Timeline

Description

This uses the new API for the Git plugin of VS Code, to provide additional details about a commit. This currently only adds a new button "Open in GitLab" to the tooltip.

Related Issues

Related to #2191 (closed)

How has this been tested?

Go to the Graph panel in the Git sidebar tab, or open a file and go to the Timeline panel in the Main sidebar tab. Hover the mouse over a commit to see additional details. The "Open in GitLab" button should be on the tooltip.

• If src/browser or src/common has been modified, please consider interoperability with the Web IDE. See Running the Extension in WebIDE.
• Consider an end-to-end test for significant new features that aren't covered by integration tests.

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