Add expires_at to property to login response

[georgevanvliet]

The current response to POST /api/login returns the following body:

{
  "id": 16,
  "name": "redacted",
  "email": "redacted@redacted.com",
  "avatar": "default.jpg",
  "api_token": "redacted",
  "created_at": "2020-01-16 18:18:57",
  "updated_at": "2020-02-06 23:52:45",
  "last_login": "2020-02-06 23:52:45",
  "policy_accepted": "beep_terms_2018_05_25_avg_v1",
  "email_verified_at": "2020-01-16 18:19:14"
}

Please add an expires_at property that indicated the expiration date of the api token.
I also notice that the dates do not have a timezone included. I suggest switching to ISO8601 format with the timezone included: YYYY-MM-DDTHH:MM:SS+/-hh:mm -> 2020-01-16T20:34:22+01:00. Preferably all dates are UTC by default, unless requirements specify otherwise.