[backend/frontend] Remove FINTEL_FOR_ENTITY feature flag (#15210)

[delemaf]

Proposed changes

• Remove FINTEL_FOR_ENTITY feature flag

Related issues

• [frontend] fix draft creation forms (#15223) #15210

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 33.15%. Comparing base (691fb26) to head (4bc2344).

Additional details and impacted files

@@                         Coverage Diff                         @@
##           issue/15366-nx-analytics-config   #15368      +/-   ##
===================================================================
- Coverage                            33.15%   33.15%   -0.01%     
===================================================================
  Files                                 3155     3155              
  Lines                               214168   214158      -10     
  Branches                             39119    39114       -5     
===================================================================
- Hits                                 71008    71003       -5     
+ Misses                              143160   143155       -5     

Flag	Coverage Δ
opencti-client-python	45.59% <ø> (ø)
opencti-front	2.86% <ø> (-0.01%)	⬇️
opencti-graphql	69.12% <100.00%> (-0.01%)	⬇️

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