Clarify that the ‘dynamic’ mode for query builders does not merge where calls

[piedrahitapablo]

Following the discussion given here, I'm creating this issue to make the "Dynamic query building" docs more clear.

The current issue is that for some reason the first time those docs are read, it's possible that people get the impression that using $dynamic() on a query enables the possibility to make multiple calls to .where(...) that are merged automatically by drizzle.

I know the docs don't state that drizzle merges the where calls and, if you read them after knowing the actual behavior, they are clear about the intent behind the $dynamic() function, but they can be improved to make more clear that .where(...) calls will keep the same behavior regarding overriding/merging.

Thanks!