Implement Rubocop rule to check `change_column_null` helper
requested to merge implement_rubocop_rule_to_check_change_column_null_for_high_traffic_tables into master
What does this MR do and why?
Using change_column_null migration helper can cause issues if it's used for a high-traffic table as it requires locking the whole table.
A recent incident related to usage of change_column_null can be seen here: gitlab-com/gl-infra/production#17730 (closed)