Add bucket to gitlab_sql_duration_seconds

The 0.25 bucket for the gitlab_sql_duration_seconds histogram
is required for calculating the Database Primary Performance
Indicator: Query apdex with 100ms target, 250ms tolerable.

lib/gitlab/metrics/subscribers/active_record.rb

@@ -22,7 +22,7 @@ module Gitlab
           return if payload[:name] == 'SCHEMA' || IGNORABLE_SQL.include?(payload[:sql])
 
           current_transaction.observe(:gitlab_sql_duration_seconds, event.duration / 1000.0) do
-            buckets [0.05, 0.1]
+            buckets [0.05, 0.1, 0.25]
           end
 
           increment_db_counters(payload)