feat(discovery/kubernetes): container_is_init label
feat(discovery/kubernetes): container_is_init label

Adds a label that shows whether the container is an init container or not

Signed-off-by: sh0rez <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@shorez.de>

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