Swagger docs: incorrect field assignments (Course)

[ShadowOfTheSpace]

• Verify the data returned by the backend and update field types from string to object where necessary
• Verify the schema with responses from our API and modify schema where necessary
• Add enum values where needed and use existing ones to replace duplications
• Update array schema (check if the courses schema isn't just an array of course and if so - delete it and replace all refs to it)
• Review and update all endpoints if needed
• Review and update the examples