[Feat]: [Add Validation for Course]

[TejasNair9977]

Description

There needs to be validation for all IDs in here. The validation must be done in the controller. You need to provide the service with a proper filter so that it can check if the ID provided in req.body actually exists for each collection that it belongs to. For example,
In req.body for adding Course, it needs to check that the provided IDs actually exist in the database. As always, never trust that the user is providing valid data.

Use Case

It will make sure that data given by the user to the database is valid.

Proposed Solution

Right before the function that creates the document, check if the IDs provided by the user is valid.