[Admin UI] User Login + Logout API

[seanpreston]

Is your feature request related to a specific problem?

To support the Fidesops Admin UI, we need endpoints to manage user authentication.

Describe the solution you'd like

POST /api/v1/login/

{
  "username": "joebloggs",
  "password": "somethingSecure"
}

{
  "authToken": ...
}

• This endpoint exchanges user login details for a token that can be used to make subsequent requests (e.g. read privacy requests currently in progress).
• The token should expire within a reasonable timeframe.
• The token should be provided by an OAuth client created especially for the admin UI.

POST /api/v1/logout/

• A logged in user hits this endpoint with their authentication token, which is then invalidated, subsequently logging the user out.