Handler for the "/catalog" endpoint to serve course data from the database.

Handler for the "/catalogs" endpoint to return the list of available catalogs.

GetListOfCatalogs retrieves distinct department codes from MongoDB.

InitMongoDB initializes the MongoDB client.

QueryCoursesFromCatalog fetches courses from the MongoDB `catalogs` collection.

QueryTermOfferings fetches offerings from the MongoDB `term_offerings` collection.

TermOfferingsHandler handles requests for term offerings.

MongoClient is the global variable for MongoDB client.