Automate Docker base image updates in the merge-train project (https://gitlab.com/gitlab-org/merge-train) by setting up renovate-bot. This will ensure the base image stays up to date with security and stability fixes while avoiding unexpected breaking changes from manual or infrequent updates. _This ticket was created from_ [_INC-4071_](https://app.incident.io/gitlab/incidents/4071) _and was automatically exported by_ [_incident.io_](https://app.incident.io) 🔥