[backend] Fix UI issue when changing organization in a user (#7682)

[CelineSebe]

Proposed changes

• replace return user in assignOrganizationToUser

Related issues

• Changing "Organizations" in a user make the page full re-render and close the drawer #7682

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

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 68.09%. Comparing base (078052e) to head (0434d76).
Report is 52 commits behind head on master.

Files	Patch %	Lines
...pencti-platform/opencti-graphql/src/domain/user.js	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8054      +/-   ##
==========================================
+ Coverage   67.75%   68.09%   +0.34%     
==========================================
  Files         572      572              
  Lines       71026    71080      +54     
  Branches     6047     6450     +403     
==========================================
+ Hits        48122    48403     +281     
+ Misses      22904    22677     -227     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[SouadHadjiat]

I have a concern about this assignOrganizationToUser, I wonder if we shouldn't use another method, or add more checks when the user is an organization admin (without SETTINGS_SET_ACCESSES).

[SouadHadjiat]

I think we should at least use findById method instead of storeLoadById which will do the right security checks.
But I also wonder if this method is usefull for an organization admin. To be checked with product team.