Investigate making an "Ember" provider

[mrchrisadams]

Ember published annual datasets of carbon intensity of electricity, based on their own analysis.

These are like the IEA, but much more liberally licensed, meaning it's much easier to bundle them into software.

Ember are an NGO listed below:

https://ember-climate.org/

And they have an annual report like this:

https://ember-climate.org/

With this permissively licensed data:
https://ember-climate.org/global-electricity-review-2021/data-explorer/

They also explain their methodology here in detail for each country they list:
https://ember-climate.org/global-electricity-review-2021/methodology/

[mrchrisadams]

@rossf7 hey Ross - Ember have started publishing data on a monthly basis now, and while it might make sense to have the local annual dataset from Ember as our default, being able to query for refresher data might be useful.

I know we already use their annual data, but I'll keep this open, as a placeholder for fetching higher time res data from them further down the line.

[rossf7]

@mrchrisadams I'm going to close this as #38 covers adding monthly data from Ember.

I moved #38 from the grid-intensity-exporter issue yesterday.