Extract method to generate series of days in measure sql classes (#29928)

app/lib/admin/metrics/measure/instance_follows_measure.rb

@@ -44,7 +44,7 @@ class Admin::Metrics::Measure::InstanceFollowsMeasure < Admin::Metrics::Measure:
         SELECT count(*) FROM new_follows
       ) AS value
       FROM (
-        SELECT generate_series(date_trunc('day', :start_at::timestamp)::date, date_trunc('day', :end_at::timestamp)::date, interval '1 day') AS period
+        #{generated_series_days}
       ) AS axis
     SQL
   end