Retrieve submissions by iid

Description

Adds a optional paramater to an already existing endpoint to filter on iid when requesting submissions.

Changes

No changes

Additions

Optional parameter

Test and Review

Closes #237

To be filled in by the reviewers

• All of the methods are commented to expectation

• The methods are tested to satisfaction

• There are no unnecessary files present in the MR

• The continuous integration has no problems with the MR

• The MR is filled in as requested (including labels, milestones, and reviewers)

• The documentation is up-to-date

• All nullable parameters are marked as such