FEATURE: Site settings defaults per locale

This change-set allows setting different defaults for different locales. 

It also:

- Adds extensive testing around site setting validation

- raises deprecation error if site setting has the default property based on env

- relocated site settings for dev and tests in the initializer

- deprecated client_setting in the site setting's loading process

- ensure it raises when a enum site setting being set

- default_locale is promoted to `required` category.

- fixes incorrect default setting and validation

- fixes ensure type check for site settings

- creates a benchmark for site setting

- sets reasonable defaults for Chinese

plugins/discourse-narrative-bot/config/settings.yml

@@ -1,8 +1,6 @@
 plugins:
   discourse_narrative_bot_enabled:
-    default:
-      default: true
-      test: false
+    default: true
     client: true
   disable_discourse_narrative_bot_welcome_post:
     default: false