[ci skip] Update guide sources for mailer view caching feature

guides/source/5_0_release_notes.md

@@ -316,6 +316,9 @@ Please refer to the [Changelog][action-mailer] for detailed changes.
 *   Template lookup now respects default locale and I18n fallbacks.
     ([commit](https://github.com/rails/rails/commit/ecb1981b))
 
+*   Template can use fragment cache like Action View template.
+    ([Pull Request](https://github.com/rails/rails/pull/22825))
+
 *   Added `_mailer` suffix to mailers created via generator, following the same
     naming convention used in controllers and jobs.
     ([Pull Request](https://github.com/rails/rails/pull/18074))
@@ -327,6 +330,9 @@ Please refer to the [Changelog][action-mailer] for detailed changes.
     the mailer queue name.
     ([Pull Request](https://github.com/rails/rails/pull/18587))
 
+*   Added `config.action_mailer.perform_caching` configuration to determine whether your templates should perform caching or not.
+    ([Pull Request](https://github.com/rails/rails/pull/22825))
+
 
 Active Record
 -------------

guides/source/action_mailer_basics.md

@@ -407,6 +407,22 @@ use the rendered text for the text part. The render command is the same one used
 inside of Action Controller, so you can use all the same options, such as
 `:text`, `:inline` etc.
 
+#### Caching mailer view
+
+You can do cache in mailer views like in application views using `cache` method.
+
+```
+<% cache do %>
+  <%= @company.name %>
+<% end %>
+```
+
+And in order to use this feature, you need to configure your application with this:
+
+```
+  config.action_mailer.perform_caching = true
+```
+
 ### Action Mailer Layouts
 
 Just like controller views, you can also have mailer layouts. The layout name

guides/source/action_view_overview.md

@@ -599,7 +599,7 @@ This would add something like "Process data files (0.34523)" to the log, which y
 
 #### cache
 
-A method for caching fragments of a view rather than an entire action or page. This technique is useful for caching pieces like menus, lists of news topics, static HTML fragments, and so on. This method takes a block that contains the content you wish to cache. See `ActionController::Caching::Fragments` for more information.
+A method for caching fragments of a view rather than an entire action or page. This technique is useful for caching pieces like menus, lists of news topics, static HTML fragments, and so on. This method takes a block that contains the content you wish to cache. See `AbstractController::Caching::Fragments` for more information.
 
 ```erb
 <% cache do %>

guides/source/configuring.md

@@ -531,6 +531,9 @@ There are a number of settings available on `config.action_mailer`:
 * `config.action_mailer.deliver_later_queue_name` specifies the queue name for
   mailers. By default this is `mailers`.
 
+* `config.action_mailer.perform_caching` specifies whether the mailer templates should perform fragment caching or not. By default this is false in all environments.
+
+
 ### Configuring Active Support
 
 There are a few configuration options available in Active Support: