Refactor: prefetch all required datasets for creation of entities from submissions

[sadiqkhoja]

Change:

Currently when there are multiple entities in a submission, our submission processing code fetches dataset information for each entity separately, even if all entities belong to the same dataset. In the PR, I have optimized that code, so now it first gets the all distinct dataset names from the submission and then fetches all of them in a single SQL command. After that the corresponding dataset information is passed downstream function.

What has been done to verify that this works as intended?

All tests are passing.

Why is this the best possible solution? Were any other approaches considered?

Nope.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

Nope.

Does this change require updates to the API documentation? If so, please update docs/api.yaml as part of this PR.

NA

Before submitting this PR, please make sure you have:

• run make test and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code from external sources are properly credited in comments or that everything is internally sourced