ignore when required variable was already added to selection

[rowe-stamy]

Added new test where the User from Accounts can have a ProductConfiguration and ProductBookmark
matched by the username field instead of id. The bug fix is to ignore if a required variable was already added.
Closes #6993 (in this specific format)

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 77.25%. Comparing base (4f56e59) to head (5b3b860).

❗ Current head 5b3b860 differs from pull request most recent head 38650f1. Consider uploading reports for the commit 38650f1 to get more accurate results

Files	Patch %	Lines
...ing/Pipeline/FieldRequirementsPlannerMiddleware.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6995   +/-   ##
=======================================
  Coverage   77.24%   77.25%           
=======================================
  Files        2632     2632           
  Lines      131361   131361           
=======================================
+ Hits       101475   101483    +8     
+ Misses      29886    29878    -8     

Flag	Coverage Δ
unittests	77.25% <0.00%> (+<0.01%)	⬆️

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[michaelstaib]

Thanks for creating this PR ... I will soon have a look.

[michaelstaib]

I will get this one in next week .... we have one massive PR that we need to merge first.