Align `TagServersMeasure` to use `WITH` query style similar to others (#29435)

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

@@ -28,14 +28,17 @@ class Admin::Metrics::Measure::TagServersMeasure < Admin::Metrics::Measure::Base
   def sql_query_string
     <<~SQL.squish
       SELECT axis.*, (
-        SELECT count(distinct accounts.domain) AS value
-        FROM statuses
-        INNER JOIN statuses_tags ON statuses.id = statuses_tags.status_id
-        INNER JOIN accounts ON statuses.account_id = accounts.id
-        WHERE statuses_tags.tag_id = :tag_id
-          AND statuses.id BETWEEN :earliest_status_id AND :latest_status_id
-          AND date_trunc('day', statuses.created_at)::date = axis.period
-      )
+        WITH tag_servers AS (
+          SELECT DISTINCT accounts.domain
+          FROM statuses
+          INNER JOIN statuses_tags ON statuses.id = statuses_tags.status_id
+          INNER JOIN accounts ON statuses.account_id = accounts.id
+          WHERE statuses_tags.tag_id = :tag_id
+            AND statuses.id BETWEEN :earliest_status_id AND :latest_status_id
+            AND date_trunc('day', statuses.created_at)::date = axis.period
+        )
+        SELECT COUNT(*) FROM tag_servers
+      ) 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
       ) as axis