[Web API issue] Track object has inconsistencies w.r.t. API documentation

[apibugsreporting]

Sometimes, track objects returned in API responses present two properties, primary_color and video_thumbnail, which are not even mentioned in the documentation. They should be documented, so that end users and developers can leverage them.

The definition of the track object that I'm referring to is here:

https://developer.spotify.com/documentation/web-api/reference/#/operations/get-track

At least, the following endpoints are affected by this issue:

- GET /playlists/{playlistId}/tracks

- GET /playlists/{playlistId}

Several test reports revealing these issues are available at the following URLs:

- http://apitesting.ddns.net/fse2022/restest/target/allure-reports/spotify_Playlists__r_rt_custom/#beh...

- http://apitesting.ddns.net/fse2022/restest/target/allure-reports/spotify_Playlists__r_rt_custom/#beh...

- http://apitesting.ddns.net/fse2022/restest/target/allure-reports/spotify_Playlists__r_rt_custom/#beh...

- http://apitesting.ddns.net/fse2022/restest/target/allure-reports/spotify_Playlists__r_rt_custom/#beh...