Add allocations to template renderer subscription

This PR adds the allocations to the instrumentation for template and
partial rendering.

Before:

```
  Rendering posts/new.html.erb within layouts/application
  Rendered posts/_form.html.erb (9.7ms)
  Rendered posts/new.html.erb within layouts/application (10.9ms)
Completed 200 OK in 902ms (Views: 890.8ms | ActiveRecord: 0.8ms)
```

After:

```
  Rendering posts/new.html.erb within layouts/application
  Rendered posts/_form.html.erb (Duration: 7.1ms | Allocations: 6004)
  Rendered posts/new.html.erb within layouts/application (Duration: 8.3ms | Allocations: 6654)
Completed 200 OK in 858ms (Views: 848.4ms | ActiveRecord: 0.4ms | Allocations: 1539564)
```

1 files changed, 12 insertions, 0 deletions

diff --git a/actionview/CHANGELOG.md b/actionview/CHANGELOG.md
index 252fce6472..fd8bae0cdf 100644
--- a/actionview/CHANGELOG.md
+++ b/actionview/CHANGELOG.md
@@ -1,3 +1,15 @@
+*   Add allocations to template rendering instrumentation.
+
+    Adds the allocations for template and partial rendering to the server output on render.
+
+    ```
+      Rendered posts/_form.html.erb (Duration: 7.1ms | Allocations: 6004)
+      Rendered posts/new.html.erb within layouts/application (Duration: 8.3ms | Allocations: 6654)
+    Completed 200 OK in 858ms (Views: 848.4ms | ActiveRecord: 0.4ms | Allocations: 1539564)
+    ```
+
+    *Eileen M. Uchitelle*, *Aaron Patterson*
+
 *   Respect the `only_path` option passed to `url_for` when the options are passed in as an array
     
     Fixes #33237.