breakManager: Allow break to be taken or delayed when overdue

breakManager: Allow break to be taken or delayed when overdue

This makes the buttons on the ‘break overdue’ notification match those
on the ‘time to take a break’ notification. This makes more sense than
showing no buttons on the former, because it leads on from the ‘time to
take a break’ notification after a short wait.

By adding a ‘Take’ button it gives the user a path to acknowledge that
they are starting to take their break, rather than having to let the
session idle.

The ‘break overdue’ notification wasn’t on the original design[1], which is
probably why its buttons got overlooked.

[1]: https://gitlab.gnome.org/Teams/Design/settings-mockups/-/blob/master/wellbeing/wellbeing.png

Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3656>