Fix performance on instances list in admin UI (#15282)

- Reduce duplicate queries
- Remove n+1 queries
- Add accounts count to detailed view
- Add separate action log entry for updating existing domain blocks

app/models/concerns/domain_materializable.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module DomainMaterializable
+  extend ActiveSupport::Concern
+
+  included do
+    after_create_commit :refresh_instances_view
+  end
+
+  def refresh_instances_view
+    Instance.refresh unless domain.nil? || Instance.where(domain: domain).exists?
+  end
+end