Simplify AddFast and avoid errgroup Commits in general
Simplify AddFast and avoid errgroup Commits in general

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