Add graphs and retention metrics to admin dashboard (#16829)

app/lib/admin/metrics/dimension/servers_dimension.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class Admin::Metrics::Dimension::ServersDimension < Admin::Metrics::Dimension::BaseDimension
+  def key
+    'servers'
+  end
+
+  def data
+    sql = <<-SQL.squish
+      SELECT accounts.domain, count(*) AS value
+      FROM statuses
+      INNER JOIN accounts ON accounts.id = statuses.account_id
+      WHERE statuses.id BETWEEN $1 AND $2
+      GROUP BY accounts.domain
+      ORDER BY count(*) DESC
+      LIMIT $3
+    SQL
+
+    rows = ActiveRecord::Base.connection.select_all(sql, nil, [[nil, Mastodon::Snowflake.id_at(@start_at)], [nil, Mastodon::Snowflake.id_at(@end_at)], [nil, @limit]])
+
+    rows.map { |row| { key: row['domain'] || Rails.configuration.x.local_domain, human_key: row['domain'] || Rails.configuration.x.local_domain, value: row['value'].to_s } }
+  end
+end