Follow-up of https://web-rca.devshift.net/incident/ITN-2024-00175

We currently rely on an SSL client certificate used for authentication purposes when we call the IT Users Service. That certificate is stored in the Vault and renewed manually.

As suggested by nmalik-srej the ITN-2024-00175 retrospective doc, we should automate the alerting and renewal process of the certificate. That kind of automation already exists in many areas. We need to examine the existing solutions and possibly leverage them in Notifications.