Harden usage_activity_by_stage.ci_builds

ci_builds: distinct_count(::Ci::Build.where(time_period), :user_id),
"usage_activity_by_stage.verify.ci_builds": -1

## get the queries on the rails console

time_period = {}
Gitlab::UsageData.distinct_count(::Ci::Build.where(time_period), :user_id)

SELECT MIN("ci_builds"."user_id") FROM "ci_builds" WHERE "ci_builds"."type" = 'Ci::Build'
https://explain.depesz.com/s/wc5a  FINE

SELECT MAX("ci_builds"."user_id") FROM "ci_builds" WHERE "ci_builds"."type" = 'Ci::Build'
https://explain.depesz.com/s/baBn FINE

SELECT COUNT(DISTINCT "ci_builds"."user_id") FROM "ci_builds" WHERE "ci_builds"."type" = 'Ci::Build' AND "ci_builds"."user_id" BETWEEN 0 AND 1250
https://explain.depesz.com/s/cY4R