Better inform user of repo errors

[AstraLuma]

When poetry fails to talk to the repository (eg PyPI), it gives the user no indication that there's network/server trouble.

Instead, you just get errors like "Unable to find installation candidates for click (8.0.3)"

[AstraLuma]

I discovered this because I tried doing poetry install during https://status.python.org/incidents/0kx5k4p9ljyw