[backend] Improve bulk Stix loader to support 100K+ relations loading in one bulk (#6386)

[richard-julien]

See #6386

[codecov]

Codecov Report

Attention: Patch coverage is 76.59574% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 66.76%. Comparing base (d857cc0) to head (f65d188).

Files	Patch %	Lines
...latform/opencti-graphql/src/database/middleware.js	68.96%	9 Missing ⚠️
...ti-platform/opencti-graphql/src/database/engine.js	88.88%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6387   +/-   ##
=======================================
  Coverage   66.76%   66.76%           
=======================================
  Files         541      541           
  Lines       64542    64569   +27     
  Branches     5306     5311    +5     
=======================================
+ Hits        43091    43110   +19     
- Misses      21451    21459    +8     

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[aHenryJard]

Tested on report up to 501 relations, work fine. I also tested the for loop protection with MAX_EVENT_LOOP_PROCESSING_TIME it's working as expected too.

I haven't tested with 100k+ relations.