(followup) Consider refactoring EntityConditionGroup into And/OrConditionGroup

This is a follow-up for #2874601-21: refactor(QueryBuilder): Improve testability/maintainability, where @e0ipso said:

2. I'd like to have a AndConditionGroup and OrConditionGroup instead of EntityConditionGroup where we need to check for the ->conjunction(). This doesn't need to be fixed here, but I'd like to see an issue linked here before merging so we don't forget.