Move default to different initializer

Is this usage correct? cc/ @prathamesh-sonpatki

guides/source/upgrading_ruby_on_rails.md

@@ -1444,18 +1444,6 @@ config.public_file_server.headers = {
 }
 ```
 
-### config/initializers/assets.rb
-
-In the most recent verison of sprockets-rails there is a flag available to configure what happens when
-an asset lookup is performed and no asset is found. By setting this value to false, an error will be
-raised so the asset lookup does not fail silently.
-
-```ruby
-# Unknown asset fallback will return the path passed in when the given
-# asset is not present in the asset pipeline.
-Rails.application.config.assets.unknown_asset_fallback = false
-```
-
 ### config/initializers/wrap_parameters.rb
 
 Add this file with the following contents, if you wish to wrap parameters into a nested hash. This is on by default in new applications.

railties/lib/rails/generators/rails/app/templates/config/initializers/assets.rb.tt

@@ -6,10 +6,6 @@ Rails.application.config.assets.version = '1.0'
 # Add additional assets to the asset load path
 # Rails.application.config.assets.paths << Emoji.images_path
 
-# Unknown asset fallback will return the path passed in when the given
-# asset is not present in the asset pipeline.
-Rails.application.config.assets.unknown_asset_fallback = false
-
 # Precompile additional assets.
 # application.js, application.css, and all non-JS/CSS in the app/assets
 # folder are already added.

railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults.rb.tt

@@ -32,3 +32,7 @@ ActiveSupport.halt_callback_chains_on_return_false = <%= options[:update] ? true
 # Configure SSL options to enable HSTS with subdomains. Previous versions had false.
 Rails.application.config.ssl_options = { hsts: { subdomains: true } }
 <%- end -%>
+
+# Unknown asset fallback will return the path passed in when the given
+# asset is not present in the asset pipeline.
+Rails.application.config.assets.unknown_asset_fallback = false