Add support in garbo prompt and schema for handling different units like tCO2, tCO2e

[Greenheart]

For example, the Swedavia report for 2023 used tCO2 as the unit instead of tCO2e like almost all other reports. The reason why this is important is because other companies may include other kinds of GHG emissions, while Swedavia 2023 only disclosed their CO2 emissions. This means their total CO2e emissions might be higher than if you only include the CO2 emissions. Thus, we can not simply convert 1 tCO2 === 1 tCO2e. Or can we? What do we do if we have other units that can't easily be converted into tCO2e?

We have support for specifying the unit in the database, but not in the garbo prompts and schemas.

The frontend will be updated separately to use the actual units, rather than a hard coded tCO2e like we could do in the beginning.