[Web API] Get data for a specific Save Code Now request

Sometimes, users are only interested in getting data for a specific Save Code Now request.

Currently, we can only retrieve the full list of save requests for a given origin and visit type by sending GET requests to the /api/1/origin/save/(visit_type)/url/(origin_url)/ endpoint.

To get data for a specific request, we could add a /api/1/origin/save/(request_id)/ endpoint for that purpose and add such URLs in the data returned by the /api/1/origin/save/(visit_type)/url/(origin_url)/ endpoint.