Eager load DB records when duplicating

[weiqingtoh]

Currently duplication of a course is done in a single transaction.
Since this duplication will take a while, to check if the transaction blocks updating of the tables.

UPDATE: because they are new objects, the transaction does not block other queries.

This issue now tracks performance improvements (e.g. number of queries needed) during duplication.

[allenwq]

The investigating reveals that the transaction won't block other operations since only new records get inserted.

But I realised that we didn't eager load the records during duplication, which leads to many N + 1 queries.

Below is an example of eager loading assessment questions when duplicate assessment, think we should do it for all other records.

duplicator.duplicate(other.assessments.includes(folder: :materials, :questions)