Enable hydra maester and clean up old cronjobs

Start using Hydra Maester instead of cronjob.

Beside this, we have to decide on how to deploy the settings for Hydra clients. Currently they are specified in flux2/core/base/single-sign-on/single-sign-on-values-configmap.yaml

We can keep it like this, unless there is a reason to change.

We can also consider only to remove the secrets from that file and let Hydra Maester generate the client IDs + secrets.