[gen4] More aggregation support

[systay]

Description

This change makes it possible for the gen4 planner to accept aggregation functions in HAVING that are not returned to the user, such as:

select id 
from tbl 
group by id 
having count(*) > 10

Checklist

• "Backport me!" label has been added if this change should be backported
• Tests were added or are not required
• Documentation was added or is not required

[github-actions]

Review Checklist

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[frouioui]

I think this is a good idea! ❤️ lgtm

[frouioui]

It would be nice to add an end-to-end test in the /queries/aggregation package and compare the results with MySQL.

[frouioui]

I love it!