Cop idea: prefer `.maximum` and `.minimum` over `.pluck` & `.max` or `.min`

## Describe the solution you'd like

https://www.fastruby.io/blog/rails/performance/writing-fast-rails-part-2 (rails 6.0)

https://blog.saeloun.com/2021/03/17/rails-enumerable-maximum-and-minimum/ (rails 7.0)

```ruby
# bad
Loan.pluck(:amount).min
Loan.pluck(:amount).max

# good
Loan.minimum(:amount)
Loan.maximum(:amount)
```


