Provide an easy method to install VS Code themes

### What would you like to be added?

There are so many great themes on the [VS Code marketplace](https://marketplace.visualstudio.com/search?target=VSCode&category=Themes&sortBy=Installs) that it would be great to have an easy to install them through the UI.

Expected behavior
1. `/install https://marketplace.visualstudio.com/items?itemName=arcticicestudio.nord-visual-studio-code`
2. Gemini downloads & extracts the theme
3. Gemini creates a configuration based on the theme and updates your settings with it

### Why is this needed?

There are a limited number of themes one can run and to setup a custom theme requires manual setup, all of which take a lot of time. We also have a lot of user requests for supporting different themes.

### Additional context

_No response_