chore: Add indexes to improve reporting performance (#9478)

- Adding a new index on (account_id,created_at,message_type) based on
our performance improvement exercise. This index significantly improves
the page load speeds of messaging reports.

db/migrate/20240516003531_add_index_for_message_type_account_date.rb

@@ -0,0 +1,7 @@
+class AddIndexForMessageTypeAccountDate < ActiveRecord::Migration[7.0]
+  disable_ddl_transaction!
+
+  def change
+    add_index :messages, [:account_id, :created_at, :message_type], name: 'index_messages_on_account_created_type', algorithm: :concurrently
+  end
+end