Resolve "Optimise container element duplication"

What is in this MR

This MR introduces a new endpoint to duplicate elements.

How to test this MR

• Create a page
• Add an element
• Duplicate the element
• Create a container element with elements inside
• Duplicate the container element

All of the duplication should work just like it did before but now we are only sending one request instead of one for each element.

Merge Request Checklist

• changelog.md has been updated if required.
• New/updated Premium/Enterprise features are separated correctly in the premium or enterprise folder
• The latest Chrome and Firefox have been used to test any new frontend features
• Documentation has been updated
• Quality Standards are met
• Performance: tables are still fast with 100k+ rows, 100+ field tables
• The redoc API pages have been updated for any REST API changes
• Our custom API docs are updated for changes to endpoints accessed via api tokens
• The UI/UX has been updated following UI Style Guide

Closes #1814 (closed)