Update the section on how to submit energy ratings

[joeyhorst]

Allowing to report more than one energy rating per asset. This is mostly to help the residential sector report more accurately on units but can be used by any other property sector as well.

Previously you had to report energy ratings under the objects energy_rating_id and energy_rating_size in the annual_data array. This will now be its own array, like building certifications.

"energy_ratings":
   [{
     "energy_rating_id": 57,
     "size": 123
   ]}

Change the instruction in https://github.com/GRESB/api-docs/blob/master/source/includes/_energy-ratings.md and update the examples in https://github.com/GRESB/api-docs/blob/master/source/includes/_assets.md. . We have to consider how we alter validation https://github.com/GRESB/api-docs/blob/master/source/includes/_validation-endpoint.md, given that _validation is returned within the new energy_ratings object and no longer in the annual_data object.