Is your enhancement related to a problem? Please describe

VS Code allows providing the extensions list (.vscode/extensions.json) that will be recommended to install once VS Code starts (docs link).

The user needs to confirm that she really wants to install the recommended extensions set.

One of the main goals of Che is to provide a fully ready environment for the developers. We can automate the step when the user needs to confirm the extensions installation. Not to bother them by accepting pop-ups, etc.

Describe the solution you'd like

With the VS Code CLI, it's possible to install the extensions set forcibly, without the user's confirmation (docs link).

One of the options: the user can provide a dedicated attribute in the Devfile to tell VS Code that the recommended extensions, provided in the .vscode/extensions.json, are actually mandatory and must be installed without the user's confirmation.