refactor: move insert_item logic out of meta_return

[thuyen]

Summary

Move insert_item logic out of meta_return into a reusable function. In a follow up, #943 will make meta_return logic even cleaner. This will make it easy for one to customize meta_return's behavior in their config.

Changes

• As title.

Checklist

I confirm that I have:

• Followed the
  Conventional Commits
  specification (e.g., feat: add new feature, fix: correct bug,
  docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with
  make test.
• Checked for breaking changes and documented them, if any.

[kristijanhusak]

Generally looks good. Let's just make it private and slightly change the name of the method.