[backend/frontend] Remove feature flag for bulk create relations (#4352)(#7500)

[aHenryJard]

Proposed changes

• Enable bulk relation

Related issues

• closes Bulk entity creation of SDO/SCO with Copy/Pasting #4352
• closes Apply the Bulk Relationship POC on all required entities #7500

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 66.21%. Comparing base (7f39a0d) to head (99752e1).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8342      +/-   ##
==========================================
- Coverage   66.21%   66.21%   -0.01%     
==========================================
  Files         597      597              
  Lines       60339    60339              
  Branches     6204     6204              
==========================================
- Hits        39956    39954       -2     
- Misses      20383    20385       +2     

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