[gitpod] configure VS Code

[akosyakov]

In next release the default Gitpod editor is going to become VS Code: https://www.gitpod.io/docs/feature-preview/#default-ide

This PR prepares gitpod configuration to be aligned with VS Code, namely:

• we decided against bloating VS Code with many built-in extensions in comparison to Theia and stick as closer as possible to the desktop configuration. Because of it cland extension should be listed explicilty.
• VS Code does not recognize settings under .gitpod.yml

Important: in production VS Code does not support yet all features like the preview, but in next release it will.