Allow concurrency when using Puma

What does this MR do?

This MR allows Rails to run concurrently when it is running in Puma.

Without this, all requests into a single worker process are locked, leading to very bad performance in the application and potentially lockups.

What are the relevant issue numbers?

#53362 (closed) is an example of the type of issue this solves.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.

Closes #53362 (closed)