Send error message when user tries to connect a GitHub repo that is already connected with another workspace

### crowd.dev edition

Cloud (hosted)

### Version

_No response_

### What happened?

When users want to connect a GitHub repo that's already been connected to crowd.dev before, the onboarding fails but the user doesn't get a notification about it.

### Command / Request

_No response_

### Relevant log output

_No response_