chore: Open Duo Chat links in browser

Description

This MR handles openLink notification from LS Duo Chat v2 plugin and opens links in the browser instead of the chat WebView.

Related Issues

Resolves gitlab-org/editor-extensions/gitlab-lsp#790 (closed)

How has this been tested?

1. Link this MR with the LS MR gitlab-org/editor-extensions/gitlab-lsp!1438 (merged)
2. Make sure you have enabled the Feature Flag that controls Duo Chat v2 . Set "gitlab.featureFlags.languageServerWebviews": true, in extension's settings.json
3. Open Duo Chat and ask it to provide you with some internal links (e.g. give me some links to GitLab docs).
4. Clicking links in chat response should open them in your default browser

⚠️ Note, that external links are not rendered nicely after this security fix. We have an issue to improve the UX for this.

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