Replace local config code with library config code (#1886)

* Replace local config code with library config code

* credo

* Update Architecture.md

* Revise since fetching logic will probably move soon

* point readers to new repo

ARCHITECTURE.md

@@ -34,7 +34,7 @@ Server:
 | Module or directory | Description |
 | - | - |
 | [`ScreenData`](/lib/screens/v2/screen_data.ex) | Common logic to answer all screen data requests. We try to keep this code agnostic of widget implementation details and free of business logic. Code changes infrequently. If a new feature is needed on _all_ screen types, the change might happen here. |
-| [`config` directory](/lib/screens/config/) | Contains modules that define the config schema for each screen type, and how to convert it to/from JSON. Most modules `use` a macro from [`config/struct.ex`](/lib/screens/config/struct.ex) to simplify defining their data structures. |
+| [`config` directory](/lib/screens/config/) | Contains modules used for caching screen configs from S3. Modules that define the config schema for each screen type, and how to convert it to/from JSON now live in the [screens-config-lib](https://github.com/mbta/screens-config-lib) repo|
 | [Candidate generators](/lib/screens/v2/candidate_generator/) | These modules define "step 1" for producing the data response for each screen type. Each one adopts the [`CandidateGenerator`](/lib/screens/v2/candidate_generator.ex) behaviour, and contains code that defines the screen's visual template as well as functions to fetch data and transform it into widgets to populate that template. |
 | [`Template`](/lib/screens/v2/template.ex) | Contains types and functions related to screen templates.  |
 | [`WidgetInstance`](/lib/screens/v2/widget_instance.ex) | Defines the common protocol that all widgets must implement. The framework code in `ScreenData` calls these protocol functions on widgets to fit them into a screen template and produce the JSON response. |

lib/screens/bus_screen_data.ex

@@ -2,12 +2,13 @@ defmodule Screens.BusScreenData do
   @moduledoc false
 
   alias Screens.Alerts.Alert
+  alias Screens.Config.State
   alias Screens.Departures.Departure
   alias Screens.LogScreenData
   alias Screens.NearbyConnections
   alias Screens.Schedules.Schedule
-  alias Screens.Config.{Bus, State}
   alias Screens.Util
+  alias ScreensConfig.Bus
 
   def by_screen_id(screen_id, is_screen, now \\ DateTime.utc_now()) do
     if State.mode_disabled?(:bus) do

lib/screens/config.ex

@@ -1,7 +1,7 @@
 defmodule Screens.Config do
   @moduledoc false
 
-  alias Screens.Config.{Devops, Screen}
+  alias ScreensConfig.{Devops, Screen}
 
   @type t :: %__MODULE__{
           screens: %{
@@ -16,7 +16,7 @@ defmodule Screens.Config do
   defstruct screens: nil,
             devops: Devops.from_json(:default)
 
-  use Screens.Config.Struct, children: [screens: {:map, Screen}, devops: Devops]
+  use ScreensConfig.Struct, children: [screens: {:map, Screen}, devops: Devops]
 
   @spec schedule_refresh_for_screen_ids(t(), list(String.t()), DateTime.t()) :: t()
   def schedule_refresh_for_screen_ids(config, screen_ids, now \\ DateTime.utc_now()) do