Configure Sourcegraph" is not actionable/helpful when repo is not found on Sourcegraph instance

Created by: felixfbecker

If a repo could not be found on Sourcegraph, the "view repo" button will show "configure Sourcegraph".

But clicking that link just opens the options page, which will indicate everything is configured properly:

We need to communicate that the repo could not be mapped correctly or doesn't exist on the instance, and how that can be solved, instead of misleading.