Is your feature request related to a problem? Please describe.
Currently the user is not notified if a certificate will expire soon.
Additionally it is not easily visible which certificates are already expired. You have to check the validity end.

Describe the solution you'd like
A notification should be sent a configurable timespan ahead of a certificate expiring.
In the certificates list view, beside the Revoked column, an additional column Expired should be added to display the expired state.

Additionally, an option to automatically renew expired certificates might be useful.