Vessel/Vehicle schema should include fuel type, and a unit for fuel type

[thomaszwagerman]

Feature Request
The vessel/vehicle schema and configurations should include something like:

"energy source": "diesel"
"power units": "tonnes"

Or

"energy source": "battery"
"power units": "Ah / day"

Abstract vehicle classes cover the implementation of calculating usage for different fuel types, but the type of fuel cannot currently be simply extracted from the route object or vehicle config.

Instead, whether SDA or Slocum use fuel or battery is decided entirely in the vessel classes, which have their own model_fuel() of model_battery() depending on which vehicle they are.

This works, but "hides" the fuel type/energy source from the user, and is only obvious once returned as a cellbox.
See bas-logist/PolarRoute-server#155.

While it works for our vehicles, this makes a flexible approach with custom vehicle of different fuel types difficult to implement.

This is would also make energy optimised routes in a front-end easier to display, as we don't have to wrangle with different terms (fuel-optimised, battery-optimised) for the same optimisation type: consumption.

It could also enable a more flexible and simplified vessel performance model. Or, for instance, "testing" different energy consumption levels for different fuel types or batteries for the same vehicle. A use case that comes to mind is sustainable aviation fuel.

Describe the solution you'd like
Vessel/vehicle configs should include a field for power source (fuel/battery), and unit (tonnes/Ah day), as shown above.

Happy to discuss semantics.