feat: add a command to restart language server

Description

Let's people restart the language server!

Demo

restart_language_server.mov

Related Issues

gitlab-org/editor-extensions/gitlab-lsp!463 (merged)

How has this been tested?

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