fix: don't forget DISTINCT for derived tables

[systay]

Description

When the planner is able to push down a derived table and everything that goes with it under a route, we were not copying over whether the SELECT was distinct or not.

Related Issue(s)

Fixes #13578

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Documentation was added or is not required

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.13%. Comparing base (4a1870a) to head (743b161).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15672   +/-   ##
=======================================
  Coverage   68.13%   68.13%           
=======================================
  Files        1556     1556           
  Lines      195028   195029    +1     
=======================================
+ Hits       132888   132890    +2     
+ Misses      62140    62139    -1     

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