add_column_with_default cop: Blacklist tables
Currently, the cop that warns about add_column_with_default... null: false
has a whitelist for small tables only.
The cop is only relevant for very large tables because execution time for adding the NOT NULL
constraint depends on the size of the table. It's likely enough for us to blacklist the larger tables (for GitLab.com scale) and don't let the cop complain about all other tables.
I don't want the cop to prevent us from adding meaningful NOT NULL
constraints to the model. We just have to be careful with large tables.