users: add is_deleted flag.

Add is_deleted flag to users table in preparation for fixing #4555.

script/fixes/125_set_users_is_deleted.rb

@@ -0,0 +1,13 @@
+#!/usr/bin/env ruby
+
+require_relative "base"
+
+with_confirmation do
+  deleted_users = User.where_regex(:name, "^user_[0-9]+~*$").where(is_deleted: false)
+
+  deleted_users.find_each do |user|
+    puts user.attributes.slice("id", "name", "level", "created_at", "last_logged_in_at").to_json
+  end
+
+  deleted_users.update_all(is_deleted: true) if ENV.fetch("FIX", "false").truthy?
+end