[frontend] add missing feature flag for import validation mode (#9300)

[JeremyCloarec]

Proposed changes

• add missing feature flag for import validation

Related issues

• [Placeholder] Ensure draft readiness for release #9300

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case (coverage and e2e)
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.29%. Comparing base (96e198d) to head (ae60176).
Report is 140 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9835      +/-   ##
==========================================
- Coverage   65.23%   64.29%   -0.95%     
==========================================
  Files         630      655      +25     
  Lines       60421    62909    +2488     
  Branches     6784     6968     +184     
==========================================
+ Hits        39417    40445    +1028     
- Misses      21004    22464    +1460     

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