Supports closed set of extensions in the WebIDE
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### Proposal
When using the WebIDE, it would be very useful to support the "auto-installation" of a predefined set of extensions.
Leveraging the usage of the [recommended extensions](https://code.visualstudio.com/docs/editor/extension-marketplace#_workspace-recommended-extensions), and ensuring that only the recommendations are installed (automatically) and that all unwantedRecommendations are automatically removed.
This helps companies to provide a default setup, matching their constraints, for any project.
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