provide Study Planet Api
Provides an instance of StudyPlanetApi using Retrofit.
This function configures and creates a Retrofit instance for interacting with the StudyPlanet API. It uses the BASE_URL as the base URL and sets up GsonConverterFactory for JSON serialization. Additionally, it uses a custom OkHttpClient configured by okhttpClient.
Return
An instance of StudyPlanetApi for making API requests.