[backend] save column selection when creating public dashboards

[labo-flg]

Add missing columns selection in public dashboard manifest.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.34%. Comparing base (6485014) to head (0d6e3ba).
Report is 8 commits behind head on release/6.5.0.

Additional details and impacted files

@@                Coverage Diff                @@
##           release/6.5.0    #9747      +/-   ##
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+ Coverage          64.29%   64.34%   +0.05%     
=================================================
  Files                653      653              
  Lines              62473    62476       +3     
  Branches            6920     6925       +5     
=================================================
+ Hits               40166    40201      +35     
+ Misses             22307    22275      -32     

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