Support "untrusted workspaces"

[gebner]

https://github.com/microsoft/vscode/issues/106488

[leodemoura]

@gebner What should we do to address this issue?

[gebner]

First we need to figure out if we need to take any action here. Basically we should not start the Lean server if the user clicks "No, I don't trust the authors", but it would be nice if syntax highlighting and the input mode still worked.