FEATURE: SKIP_DB_AND_REDIS env var (#7756)

Sometimes we would like to create a base image without any DB access, this
assists in creating custom base images with custom plugins that already
includes `public/assets`

Following this change set you can run:

```
SPROCKETS_CONCURRENT=1 DONT_PRECOMPILE_CSS=1 SKIP_DB_AND_REDIS=1 RAILS_ENV=production bin/rake assets:precompile
```

Then it is straight forward to create a base image without needing a DB or
Redis.

lib/freedom_patches/translate_accelerator.rb

@@ -138,6 +138,8 @@ module I18n
     def overrides_by_locale(locale)
       return unless @overrides_enabled
 
+      return {} if GlobalSetting.skip_db?
+
       site = RailsMultisite::ConnectionManagement.current_db
 
       by_site = @overrides_by_site[site]