Adjust SQL and transaction Prometheus buckets

This allows us to better calculate Apdex scores, instead of having to
use the 0.1 and 1.0 buckets.

changelogs/unreleased/sql-buckets.yml

+---
+title: Adjust SQL and transaction Prometheus buckets
+merge_request:
+author:
+type: other

lib/gitlab/metrics/subscribers/active_record.rb

@@ -20,7 +20,7 @@ module Gitlab
         define_histogram :gitlab_sql_duration_seconds do
           docstring 'SQL time'
           base_labels Transaction::BASE_LABELS
-          buckets [0.001, 0.01, 0.1, 1.0, 10.0]
+          buckets [0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0]
         end
 
         def current_transaction

lib/gitlab/metrics/transaction.rb

@@ -140,7 +140,7 @@ module Gitlab
       define_histogram :gitlab_transaction_duration_seconds do
         docstring 'Transaction duration'
         base_labels BASE_LABELS
-        buckets [0.001, 0.01, 0.1, 1.0, 10.0]
+        buckets [0.1, 0.25, 0.5, 1.0, 2.5, 5.0]
       end
 
       define_histogram :gitlab_transaction_allocated_memory_bytes do