Changed category fields in /courses endpoint

[ArtemHolikov]

Problem: Some category fields have an object with fields as an example, some have just string with id. Check courseService and update those examples with real values from API

Now: category fields changed to actual API response

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ShadowOfTheSpace]

Please, check the references in cource-schema.yaml file. You are assigning a reference to a string field and, also they are not from components, you added them as definition.

[ArtemHolikov]

Please, check the references in cource-schema.yaml file. You are assigning a reference to a string field and, also they are not from components, you added them as definition.

As I know, we return just id as a string, that's why it assigned as a string. And added ref to show which object we receive via this id. Regarding to problem with components/definitions, it's already done in my other PR. It defined as definitions