Intercept Arel calls to suggest indexes

Intercept Arel querys to allow query specific indexes. Maybe something like this:

```ruby
LolDba.suggest_index do
  Customer.where(name: 'Diego')
end
```
And we suggest an index on `name`

related:
https://github.com/rails/rails/tree/master/activerecord/lib/arel