Retrieve merge request approvers via API

Description

According to the linked merge request, the UI will be extended to filter by merge request approvers. At the moment it is also not possible to get information about approvers via API.

~"feature proposal"

Proposal

API should be extended by the possibility to retrieve approver information. Response GET /projects/:id/merge_requests/:merge_request_id/approvals could be extended by "approvers" to get all approvers, no matter if they already approved or not.

{
  "id": 5,
  "iid": 5,
  "project_id": 1,
  "title": "Approvals API",
  "description": "Test",
  "state": "opened",
  "created_at": "2016-06-08T00:19:52.638Z",
  "updated_at": "2016-06-08T21:20:42.470Z",
  "merge_status": "can_be_merged",
  "approvals_required": 2,
  "approvals_missing": 1,
  "approved_by": [
    {
      "user": {
        "name": "Administrator",
        "username": "root",
        "id": 1,
        "state": "active",
        "avatar_url": "http://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80\u0026d=identicon",
        "web_url": "http://localhost:3000/u/root"
      }
    }
  ]
"approvers":[
 {
  "user":{
   ...  
  }
 }
]
}

Links / references