Use a REST API call instead of Automation for Users.current_user()

There are several ways to retrieve informations about the logged user:

• POST site/automation/login (Automation, currently used), it returns:

  {
    "entity-type": "login",
    "username": "Administrator",
    "isAdministrator": true,
    "groups": [
      "administrators"
    ]
  }

• GET site/api/v1/me (REST API), it returns:

  {
    "entity-type": "user",
    "id": "Administrator",
    "properties": {
      "firstName": "",
      "lastName": "",
      "tenantId": null,
      "groups": [
        "administrators"
      ],
      "company": "",
      "email": "devnull@nuxeo.com",
      "username": "Administrator"
    },
    "extendedGroups": [
      {
        "name": "administrators",
        "label": "Administrators group",
        "url": "group/administrators"
      }
    ],
    "isAdministrator": true,
    "isAnonymous": false
  }

Let's move to the GET approach, no need to POST data for such information.

It will also fix the current behavior: as of now a User model is created, but the retrieved entity-type is login and not user, so the current object is lacking of data.