Document new status API endpoints (#6262)
Document new status API endpoints (#6262)

* Document new status API endpoints

These were added in https://github.com/prometheus/prometheus/pull/6243
for the React UI.

Signed-off-by: Julius Volz <d7748b1e6f41fd74500c5ccae0980eab88c2ef61@gmail.com>

* Update new-in notices

Signed-off-by: Julius Volz <d7748b1e6f41fd74500c5ccae0980eab88c2ef61@gmail.com>

prometheus/prometheus,prometheus/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,alileza/prometheus,kangwoo/prometheus,Gouthamve/prometheus,keegancsmith/prometheus,alileza/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,Gouthamve/prometheus,Gouthamve/prometheus,alileza/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,keegancsmith/prometheus,kangwoo/prometheus,prometheus/prometheus,alileza/prometheus,keegancsmith/prometheus