Add final stage to the logic of physical plan planning

[metalmatze]

Instead of adding the final stage boolean to the physical plan execution, I think this logic should be part of the physical plan planning. i.e. when planning a multi-stage count, instead of planning a count(final=true) operator, you would just plan a sum() operator at the final stage.

Originally posted by @asubiotto in #202 (comment)

[github-actions]

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[asubiotto]

I think this would still be worth keeping open, we should remove the booleans from the constructor and instead have the physical planner create these aggregations.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.