Introducing the new CLI for VSTS

Introduces a new cross-platform command-line interface (CLI) for Visual Studio Team Services (VSTS) and Team Foundation Server (TFS). The CLI is in preview and supports managing pull requests, work items, builds, and more. It runs on Windows, Linux, and macOS, is available as a Docker image, integrates with the Git CLI (e.g., `git pr create`), and shares a platform with the Azure CLI. The project is open source on GitHub, inviting community contributions. Documentation for installation and getting started is provided.