This commit implements a new widget in mail, `StatusBarDurationField`. Purpose:
seeing how long a record has spent in each stage in a form view.
It is implemented for records with a `many2one` status field and gets the data
from the `duration_tracking` field of the record. `duration_tracking` is computed
by adding the `mail.tracking.duration.mixin` to a model.
Time is shown using a luxon Duration object. "narrow" specifies that time is
expressed with one character and luxon takes care of translations.
Task-3032773
Part-of: odoo/odoo#108554
