Adding support for emission factor for grid consumption per region

[adriaan]

The current emissionfactor endpoints return emission factors for generation within the region.

My use case is high-resolution carbon accounting, i.e. calculating emissions related to electricity imported from the grid in a highly granular fashion (sub 1-hour intervals). For this use case I need the emission factor for consumption from the grid, i.e. the emission factor based on both generation within the region and imports from other regions.

With emission factors varying widely between states, imports can have a big impact on the emission factor for grid consumption (e.g. Tasmania's emission factor for consumption is heavily impacted by imports from Victoria)

It would be great if the API supported this type of emission factor (possibly through a query param on the current emissionfactor endpoints.