Description:

Generates two new database migrations which will safely add a check that
a column is not null, and validate it separately.

Example:

rails generate nandi:not_null_check foos bar

This will create:
    db/safe_migrations/20190424123727_add_not_null_check_on_bar_to_foos.rb
    db/safe_migrations/20190424123728_validate_not_null_check_on_bar_to_foos.rb

Example:

rails generate nandi:not_null_check foos bar --validation-timeout 20000

This will create:
    db/safe_migrations/20190424123727_add_not_null_check_on_bar_to_foos.rb
    db/safe_migrations/20190424123728_validate_not_null_check_on_bar_to_foos.rb

The statement timeout in the second migration will be set to 20,000ms.