[backend] keep increasing back pressure delay if queue size keeps increasing (#9358)

[JeremyCloarec]

Proposed changes

• before, we only increased connection delay once in manageBackPressure. We now keep increasing the delay if the first delay increase wasn't enough to be able to reduce current queue size

Related issues

• Memory leak when ingesting an opencti stream configured with an empty starting synchronization date #9358

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 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 65.13%. Comparing base (7180d27) to head (db97bae).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
...latform/opencti-graphql/src/manager/syncManager.js	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9555      +/-   ##
==========================================
- Coverage   65.13%   65.13%   -0.01%     
==========================================
  Files         630      630              
  Lines       60147    60150       +3     
  Branches     6703     6705       +2     
==========================================
- Hits        39179    39176       -3     
- Misses      20968    20974       +6     

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