add project_id to identifications API endpoint

Platform(s): API

URLs: NA

Description of need:
I attended a meeting for Los Angeles City Nature Challenge. The organizers mentioned they want to emphasize identifications for upcoming CNC. They discussed maybe getting the number of identifications for each CNC projects.

I looked at the iNaturalist API v1/identifications endpoint, and project_id is not one available params. Without the ability to filter identifications by project_id, it will be time consuming for CNC organizers to get the number of identifications per project. I think they would need to download all the observations for a project, and sum up identifications_count.

Feature request details:

I propose adding project_id that accepts one or more ids to v1/identifications. This already exists for observations endpoint. That way people can get the identifications for a project using the API.

Proposed API

https://api.inaturalist.org/v1/identifications?project_id=224219
https://api.inaturalist.org/v1/identifications?project_id=224219,226032

The api would return.

{
  "total_results": xxx,
  "page":1,
  "per_page":30,
  "results":[...]
}

To get just the identifications count for a project without getting individual identifications, people can set per_page=0

https://api.inaturalist.org/v1/identifications?project_id=224219&per_page=0

{
  "total_results": 1234,
  "page":1,
  "per_page":0,
  "results":[]
}