Unity catalog access token automatically fetched

[ion-elgreco]

Access tokens can't be generated from the UI, and through APIs we can't generate them long enough.

It would be easier if LakeFS used the Azure entra service principal to just generate a short lived access token and pass that to the unity catalog exporter.

Implication of not adding this, means some one has to write a script that constantly fetches a new token before the other one expires, then update the k8s secret and restart the pod..