Currently omnisharp.path and omnisharp.useGlobalMono cannot be overridden at the workspace level.
Reason for change:
Currently, due to an architectural issue in roslyn, omnisharp's scripting support does not support custom scripting hosts. Because of this a custom omnisharp build must be used in order to use a custom scripting host. The problem with that is the omnisharp implementation is global.
Allowing omnisharp.path would allow the omnisharp implementation to be overridden only where needed.
The reason for needing omnisharp.useGlobalMono is because setting it to never is the only way to run a custom omnisharp build without mono. My current omnisharp build doesn't use mono (.net 5 instead).
Having these two settings available at the workspace level would allow the vscode extension to be used in custom scripting scenarios without affecting the normal operation machine wide.